While it's obviously no easier, the ability to add constraints would probably work for what most people are looking for there, given the nature of parts designed in MoI. That said, with all of the new geometric intercepts, you're most of the way there. Possible, you could leverage the new style and group system -- pull up an object in there, get a list of all of its existing geometric relationships, and tell the system to enforce some of them. If you added a way to have construction planes, lines, and points stick around more, that would get you most of the rest; you could even do distance bounding constraints as being between two points on a cline. There'd still be some things that wouldn't cover, of course -- relative size constraints, for instance, although most of those cases could probably be handled by showing a list of the other constraints the current constraint could establish a relationship with.

That said, yes, big, big chunk of work, and probably a v4+ thing, I'm sure, but I'm another person who would love it, especially coupled with API additions aimed at making generative shape creation easier.