With https://bugs.eclipse.org/bugs/show_bug.cgi?id=434185 , WTP Server Discovery mechanism was granted a new strategy which allows to rely on regular p2 metadata instead of a site.xml.
Support for this was already merged in server ( https://github.com/jbosstools/jbosstools-server/commit/2d3cc63a9b67753ad92a7bbcda15e1d15b2e22a8 )

In order to save an artifact to manage (the webtools p2 repository), we could use this mechanism and consider contributing directly the main JBT URL to webtools discovery.

However, server discovery also keeps older strategies and since we produce invalid site.xml files, this is currently failing

!ENTRY org.eclipse.equinox.p2.updatesite 2 0 2015-05-04 09:40:58.088
!MESSAGE Error parsing feature stream. The unique identifier or the version is null or empty for the State: "Category": unique identifier="minimal-json" version="null".

because we are lines specifying bundle but no version in the site.xml.

nickboldt What are those site.xml useful for? Could we get rid of them?