Perhaps I missed your point.
Tim, I could've sworn that you had been following the IETF ION WG
mailing list, where this has been discussed on hundreds of occasions.
I hesitate to even mention this on NANOG (I really don't want to
re-hash this on this list), but I can't hold my tongue.
The scalability of an ATM network where each end-point is fully meshed
to all other end-points decreases in direct proportion to the number
of end-points. This is not so much a layer 2 problem, per se, but rather
the ability to maintain functional routing (convergence, et al.) in a
fully meshed network topology.
This does not scale.