>>>But the whole thing is such a messy area to work with, that I may just not really be able to support it at all, I'm not really sure yet.

although will have been great to have in MoI, you are right to say is such a messy area, Perhaps is wise to forget about it, at list until autodesk sorts it out, if they ever do.

>>>I hope they do implement that for Revit as well, that would certainly be a big help.

I think they Should, Rhino+Revit is a common combo in AEC...

>>>I'm not sure if that would work or not - does OpenDGN support general trimmed NURBS surfaces and solids?

All I can tell Microstation is a robust modeler which runs on Parasolid Modeling Kernel...I'm not sure if that is any help.

>>>Maybe in the future when I have opened things up so that third parties can extend MoI more easily with import/export plugins, someone with more patience than me will be able to develop a plugin for some of these things.

By saying opened things up, do you mean SDK?
In which Version of MoI you think you may releasing a SDK?
(off topic) I'm dreaming of a T-Splines connection or something similar.