Jonathan,
I have not said anything about generic B2BUAs here. Each B2BUA
implementation will need to have its own record (and server) of what it is
transparent to or not. It would not be a generic list.
Perhaps it is reasonable to remove the B2BUA definition, since there is no
definition of a gateway and they are similar beasts. Just as long as such
an action does not imply that SIP is not suitable for a certain class of
problem.
Removal of the definition has nothing at all to do with whether or not
such a SIP application can be built. Clearly it can.