@Transactional is being developed as part of a JTA maintenance release. It will live in the package javax.transaction. If you have any issue with this, please contact Linda DeMichel with your feedback (please cc me). Putting comments on this issue won't help
I think the current plan is for @Transactional to be meta-annotated with @InterceptorBinding. If you see a problem with this, then there is an alternative option, which is for it to be made an interceptor binding at CDI deployment time using the CDI SPI. Again, Linda is the person to address this feedback to.
Currently all scopes are defined in CDI. I'm perfectly open to addressing whether they should be moved out, but that is another discussion. On this basis, @TransactionScoped is being considered as part of CDI.
@Transactional is proposed to have a single member, transactionType, which will be an enum of TransactionType. TransactionType is identical TransactionAttributeType, and indeed @Transactional is identical to @TransactionAttribute. However the plan is to add new, identical annotations and NOT to move the existing TransactionAttribute and TransactionAttributeType. This can't be done due to backwards compatibility requirements.
There is also an extensive discussion on how EJB CMT should interact with the new @Transactional, which I would strongly recommend getting involved with, as currently we are having to choose between a set of bad options.