A possible way to implement / specify this would be to reuse the javax.ejb.TransactionAttribute annotation but handle it as InterceptorBinding in CDI beans.
So instead of @Transactional(transaction=REQUIRES_NEW)
we could use @javax.ejb.TransactionAttribute(value=REQUIRES_NEW)
javax.ejb.TransactionAttribute is a simple annotation atm. We could add this as interceptor binding via our CDI Extension SPI
I'm not sure though what that would mean for EJBs in return. They would have to ignore this special Interceptor if the annotation is applied on an EJB.