I know I've invested a lot of time in taming that ***** to approximate my vB3 layout in 4.x, and after much griping and sniping now the users are used to vB4. Dropping some new, simpler, completely different thing on them is going to give me another month of calming people down and explaining why change is good.
Most of you are looking at this from a forum owner's point of view, and from there, yeah, this is all great news and fun and sunflowers and candy canes. But I don't think your users are going to share your enthusiasm. Especially if you recently dragged them through a painful vB 4.x upgrade.