This is all interesting stuff even if, at the moment, somewhat academic.
With just the two coders it is hard to find time to get the bits we really want to do in place! We are sorely missing an MU coder which means our support for MU is limited and why, officially we don't really make the claim that SPF is MU compatible… just in case! Sometimes, MU seems to go it's own way on things which makes it even more difficult.
There is however, talk in the WP camp of combining standard WP and MU back into one application which would probably be a good thing and of and when that happens we may be better placed.