I'm attaching a WAR to reproduce this problem. The name of the WAR is that same as the one in JBAS-8908, but it is quite different in that it WAR includes Facelets 1.1.15.B1 and ajax4jsf. You can work around the problem if you set
<context-param>
<param-name>com.sun.faces.validateXml</param-name>
<param-value>false</param-value>
</context-param>

You can also work around the problem if you add "system" as a dependency of com.sun.jsf-impl.

However, with the context param set to true and without "system", you get this classloading error:

14:17:18,236 INFO [javax.enterprise.resource.webcontainer.jsf.config] (MSC service thread 1-1) Unsanitized stacktrace from failed start...: com.sun.faces.config.ConfigurationException: java.util.concurrent.ExecutionException: com.sun.faces.config.ConfigurationException: Unable to parse document 'vfs:/C:/as7trunk/jboss-as/build/target/jboss-7.0.0.Alpha2/bin/content/mojarra2.0-notbundled.war/WEB-INF/lib/ajax4jsf-1.1.1.jar/META-INF/faces-config.xml': Translet class loaded, but unable to create translet instance.
at com.sun.faces.config.ConfigManager.getConfigDocuments(ConfigManager.java:673) file:C:%5Cas7trunk%5Cjboss-as%5Cbuild%5Ctarget%5Cjboss-7.0.0.Alpha2%5Cmodules%5Ccom%5Csun%5Cjsf-impl%5Cmain%5Cjsf-impl-2.0.4-b09.jar:2.0.4-b09
at com.sun.faces.config.ConfigManager.initialize(ConfigManager.java:309) file:C:%5Cas7trunk%5Cjboss-as%5Cbuild%5Ctarget%5Cjboss-7.0.0.Alpha2%5Cmodules%5Ccom%5Csun%5Cjsf-impl%5Cmain%5Cjsf-impl-2.0.4-b09.jar:2.0.4-b09
at com.sun.faces.config.ConfigureListener.contextInitialized(ConfigureListener.java:226) file:C:%5Cas7trunk%5Cjboss-as%5Cbuild%5Ctarget%5Cjboss-7.0.0.Alpha2%5Cmodules%5Ccom%5Csun%5Cjsf-impl%5Cmain%5Cjsf-impl-2.0.4-b09.jar:2.0.4-b09
at org.apache.catalina.core.StandardContext.contextListenerStart(StandardContext.java:3369) file:C:%5Cas7trunk%5Cjboss-as%5Cbuild%5Ctarget%5Cjboss-7.0.0.Alpha2%5Cmodules%5Corg%5Cjboss%5Cas%5Cweb%5Cmain%5Cjbossweb-7.0.0.Beta2.jar:7.0.0.Alpha2-SNAPSHOT
at org.apache.catalina.core.StandardContext.start(StandardContext.java:3828) file:C:%5Cas7trunk%5Cjboss-as%5Cbuild%5Ctarget%5Cjboss-7.0.0.Alpha2%5Cmodules%5Corg%5Cjboss%5Cas%5Cweb%5Cmain%5Cjbossweb-7.0.0.Beta2.jar:7.0.0.Alpha2-SNAPSHOT
at org.jboss.as.web.deployment.WebDeploymentService.start(WebDeploymentService.java:61) file:C:%5Cas7trunk%5Cjboss-as%5Cbuild%5Ctarget%5Cjboss-7.0.0.Alpha2%5Cmodules%5Corg%5Cjboss%5Cas%5Cweb%5Cmain%5Cjboss-as-web-7.0.0.Alpha2-SNAPSHOT.jar:7.0.0.Alpha2-SNAPSHOT
at org.jboss.msc.service.ServiceControllerImpl$StartTask.run(ServiceControllerImpl.java:1367)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886) [:1.6.0_18]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908) [:1.6.0_18]
at java.lang.Thread.run(Thread.java:619) [:1.6.0_18]
Caused by: java.util.concurrent.ExecutionException: com.sun.faces.config.ConfigurationException: Unable to parse document 'vfs:/C:/as7trunk/jboss-as/build/target/jboss-7.0.0.Alpha2/bin/content/mojarra2.0-notbundled.war/WEB-INF/lib/ajax4jsf-1.1.1.jar/META-INF/faces-config.xml': Translet class loaded, but unable to create translet instance.
at java.util.concurrent.FutureTask$Sync.innerGet(FutureTask.java:222) [:1.6.0_18]
at java.util.concurrent.FutureTask.get(FutureTask.java:83) [:1.6.0_18]
at com.sun.faces.config.ConfigManager.getConfigDocuments(ConfigManager.java:671) file:C:%5Cas7trunk%5Cjboss-as%5Cbuild%5Ctarget%5Cjboss-7.0.0.Alpha2%5Cmodules%5Ccom%5Csun%5Cjsf-impl%5Cmain%5Cjsf-impl-2.0.4-b09.jar:2.0.4-b09
... 9 more
Caused by: com.sun.faces.config.ConfigurationException: Unable to parse document 'vfs:/C:/as7trunk/jboss-as/build/target/jboss-7.0.0.Alpha2/bin/content/mojarra2.0-notbundled.war/WEB-INF/lib/ajax4jsf-1.1.1.jar/META-INF/faces-config.xml': Translet class loaded, but unable to create translet instance.
at com.sun.faces.config.ConfigManager$ParseTask.call(ConfigManager.java:845) file:C:%5Cas7trunk%5Cjboss-as%5Cbuild%5Ctarget%5Cjboss-7.0.0.Alpha2%5Cmodules%5Ccom%5Csun%5Cjsf-impl%5Cmain%5Cjsf-impl-2.0.4-b09.jar:2.0.4-b09
at com.sun.faces.config.ConfigManager$ParseTask.call(ConfigManager.java:790) file:C:%5Cas7trunk%5Cjboss-as%5Cbuild%5Ctarget%5Cjboss-7.0.0.Alpha2%5Cmodules%5Ccom%5Csun%5Cjsf-impl%5Cmain%5Cjsf-impl-2.0.4-b09.jar:2.0.4-b09
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303) [:1.6.0_18]
at java.util.concurrent.FutureTask.run(FutureTask.java:138) [:1.6.0_18]
at com.sun.faces.config.ConfigManager.getConfigDocuments(ConfigManager.java:659) file:C:%5Cas7trunk%5Cjboss-as%5Cbuild%5Ctarget%5Cjboss-7.0.0.Alpha2%5Cmodules%5Ccom%5Csun%5Cjsf-impl%5Cmain%5Cjsf-impl-2.0.4-b09.jar:2.0.4-b09
... 9 more
Caused by: javax.xml.transform.TransformerConfigurationException: Translet class loaded, but unable to create translet instance.
at com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl.defineTransletClasses(TemplatesImpl.java:335) [:1.6.0_18]
at com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl.getTransletInstance(TemplatesImpl.java:349) [:1.6.0_18]
at com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl.newTransformer(TemplatesImpl.java:382) [:1.6.0_18]
at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerFactoryImpl.newTransformer(TransformerFactoryImpl.java:618) [:1.6.0_18]
at com.sun.faces.config.ConfigManager$ParseTask.getTransformer(ConfigManager.java:1007) file:C:%5Cas7trunk%5Cjboss-as%5Cbuild%5Ctarget%5Cjboss-7.0.0.Alpha2%5Cmodules%5Ccom%5Csun%5Cjsf-impl%5Cmain%5Cjsf-impl-2.0.4-b09.jar:2.0.4-b09
at com.sun.faces.config.ConfigManager$ParseTask.getDocument(ConfigManager.java:930) file:C:%5Cas7trunk%5Cjboss-as%5Cbuild%5Ctarget%5Cjboss-7.0.0.Alpha2%5Cmodules%5Ccom%5Csun%5Cjsf-impl%5Cmain%5Cjsf-impl-2.0.4-b09.jar:2.0.4-b09
at com.sun.faces.config.ConfigManager$ParseTask.call(ConfigManager.java:836) file:C:%5Cas7trunk%5Cjboss-as%5Cbuild%5Ctarget%5Cjboss-7.0.0.Alpha2%5Cmodules%5Ccom%5Csun%5Cjsf-impl%5Cmain%5Cjsf-impl-2.0.4-b09.jar:2.0.4-b09
... 13 more

14:17:18,329 SEVERE [javax.enterprise.resource.webcontainer.jsf.config] (MSC service thread 1-1) Critical error during deployment: : com.sun.faces.config.ConfigurationException: CONFIGURATION FAILED! Translet class loaded, but unable to create translet instance.
at com.sun.faces.config.ConfigManager.initialize(ConfigManager.java:357) file:C:%5Cas7trunk%5Cjboss-as%5Cbuild%5Ctarget%5Cjboss-7.0.0.Alpha2%5Cmodules%5Ccom%5Csun%5Cjsf-impl%5Cmain%5Cjsf-impl-2.0.4-b09.jar:2.0.4-b09
at com.sun.faces.config.ConfigureListener.contextInitialized(ConfigureListener.java:226) file:C:%5Cas7trunk%5Cjboss-as%5Cbuild%5Ctarget%5Cjboss-7.0.0.Alpha2%5Cmodules%5Ccom%5Csun%5Cjsf-impl%5Cmain%5Cjsf-impl-2.0.4-b09.jar:2.0.4-b09
at org.apache.catalina.core.StandardContext.contextListenerStart(StandardContext.java:3369) file:C:%5Cas7trunk%5Cjboss-as%5Cbuild%5Ctarget%5Cjboss-7.0.0.Alpha2%5Cmodules%5Corg%5Cjboss%5Cas%5Cweb%5Cmain%5Cjbossweb-7.0.0.Beta2.jar:7.0.0.Alpha2-SNAPSHOT
at org.apache.catalina.core.StandardContext.start(StandardContext.java:3828) file:C:%5Cas7trunk%5Cjboss-as%5Cbuild%5Ctarget%5Cjboss-7.0.0.Alpha2%5Cmodules%5Corg%5Cjboss%5Cas%5Cweb%5Cmain%5Cjbossweb-7.0.0.Beta2.jar:7.0.0.Alpha2-SNAPSHOT
at org.jboss.as.web.deployment.WebDeploymentService.start(WebDeploymentService.java:61) file:C:%5Cas7trunk%5Cjboss-as%5Cbuild%5Ctarget%5Cjboss-7.0.0.Alpha2%5Cmodules%5Corg%5Cjboss%5Cas%5Cweb%5Cmain%5Cjboss-as-web-7.0.0.Alpha2-SNAPSHOT.jar:7.0.0.Alpha2-SNAPSHOT
at org.jboss.msc.service.ServiceControllerImpl$StartTask.run(ServiceControllerImpl.java:1367)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886) [:1.6.0_18]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908) [:1.6.0_18]
at java.lang.Thread.run(Thread.java:619) [:1.6.0_18]
Caused by: javax.xml.transform.TransformerConfigurationException: Translet class loaded, but unable to create translet instance.
at com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl.defineTransletClasses(TemplatesImpl.java:335) [:1.6.0_18]
at com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl.getTransletInstance(TemplatesImpl.java:349) [:1.6.0_18]
at com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl.newTransformer(TemplatesImpl.java:382) [:1.6.0_18]
at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerFactoryImpl.newTransformer(TransformerFactoryImpl.java:618) [:1.6.0_18]
at com.sun.faces.config.ConfigManager$ParseTask.getTransformer(ConfigManager.java:1007) file:C:%5Cas7trunk%5Cjboss-as%5Cbuild%5Ctarget%5Cjboss-7.0.0.Alpha2%5Cmodules%5Ccom%5Csun%5Cjsf-impl%5Cmain%5Cjsf-impl-2.0.4-b09.jar:2.0.4-b09
at com.sun.faces.config.ConfigManager$ParseTask.getDocument(ConfigManager.java:930) file:C:%5Cas7trunk%5Cjboss-as%5Cbuild%5Ctarget%5Cjboss-7.0.0.Alpha2%5Cmodules%5Ccom%5Csun%5Cjsf-impl%5Cmain%5Cjsf-impl-2.0.4-b09.jar:2.0.4-b09
at com.sun.faces.config.ConfigManager$ParseTask.call(ConfigManager.java:836) file:C:%5Cas7trunk%5Cjboss-as%5Cbuild%5Ctarget%5Cjboss-7.0.0.Alpha2%5Cmodules%5Ccom%5Csun%5Cjsf-impl%5Cmain%5Cjsf-impl-2.0.4-b09.jar:2.0.4-b09
at com.sun.faces.config.ConfigManager$ParseTask.call(ConfigManager.java:790) file:C:%5Cas7trunk%5Cjboss-as%5Cbuild%5Ctarget%5Cjboss-7.0.0.Alpha2%5Cmodules%5Ccom%5Csun%5Cjsf-impl%5Cmain%5Cjsf-impl-2.0.4-b09.jar:2.0.4-b09
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303) [:1.6.0_18]
at java.util.concurrent.FutureTask.run(FutureTask.java:138) [:1.6.0_18]
at com.sun.faces.config.ConfigManager.getConfigDocuments(ConfigManager.java:659) file:C:%5Cas7trunk%5Cjboss-as%5Cbuild%5Ctarget%5Cjboss-7.0.0.Alpha2%5Cmodules%5Ccom%5Csun%5Cjsf-impl%5Cmain%5Cjsf-impl-2.0.4-b09.jar:2.0.4-b09
at com.sun.faces.config.ConfigManager.initialize(ConfigManager.java:309) file:C:%5Cas7trunk%5Cjboss-as%5Cbuild%5Ctarget%5Cjboss-7.0.0.Alpha2%5Cmodules%5Ccom%5Csun%5Cjsf-impl%5Cmain%5Cjsf-impl-2.0.4-b09.jar:2.0.4-b09
... 8 more

It has been verified that the TCCL is properly set when ConfigManger calls getTransformer(). Also, several attempts have been made to add other dependencies besides "system".