general_objects is very useful for mapping ACS 3'ish stuff to objects if you ever have the need (I haven't but it would be useful!)
A simple "object proxy" as Dean talks about wouldn't have to be generalized and would be simple. Dean and I have talked a bit about this, and as Ben states he and I have talked about the general issue.
Ben ... one reason we've discussed this "proxy object" style of solving the problem is backwards compatibility. We don't want to break existing sites nor do we want to provide a difficult upgrade facility. If someone comes up with a simple way to alter the datamodel on an existing site to something that makes object types 100% objects I'd be more than willing to drop Dean's suggestion, which is an admitted kludge.
But it's the same kludge I've been kicking around ...
More elegant kludges are welcome, too ... though as kludges go this one's not bad!
But a ground-up redesign of how object types are declared and used in the system may be impossible at the moment, particularly considering that PG's "alter" capabilities are somewhat weak.
I'd love to be proven wrong, of course!