Features will probably be an updated profile page including a UBB buddy list, visitor comments to the profile itself, and blogs. List of recent blogs on the main profile page, linking to the full blog post with user comments beneath. Some type of user control for the profile owner to edit/delete comments, with the forum admin being able to do so as well.
As for not working on both at the same time. Couple reasons for this. As mentioned we've been promising blogs for a long time now. At this point I'm not sure if we'll be doing the UI update in one swoop. We may be splitting it into a Control Panel update first and then the front end second. If that were the case it would be 2 versions until blogs would get put in.
It's not totally doubling the work. The database work and interaction between scripts and DB won't have to be redone, just the design. When we do the UI update you can expect the blog to expand in features a bit. Probably giving the owner the option to what columns are displayed on the right/left side, etc.
