IMHO the issue I see with leaving these out is the transition
mechanism
becomes a solution for only the most basic of "web" type services.
While this makes the solution simple, it removes the motivation for
IPv6 within the 3GPP network. It is important to at least match or
mimic the functionality available in the IPv4 domain.
Tunnelling in 3GPP is not intended to provide full emulation of
the native IPv4 or native IPv6 services, since that would basically require
full dual IP support in all related 3GPP signalling interfaces.