Ditto, all sound great!
Especially the email, lists / edit users and the stats... funky!
In a world where anything was possible (:o) I'd quite like these kind of features too:
-Automated blog filtering techniques (i.e. calls for 'latest blogs', 'latest updated blogs' etc. ... which could also be put up on the homepage)
-Allow different amounts of storage space to each user (and group) and control over what files they are / aren't able to upload as a group.
-Something that allows you to twiddle with the default settings on new blogs. For example, older versions of WPMU (like the last stable) have had 'email me when comments are held for moderation' unticked... and while that's cool, I'd quite like with some groups to default set that to ticked without having to hack the files
-Not having really got it going yet I'm not sure if you have it there but being able to propagate plugins (like subscribe to comments or subscribe2) would be a really cool thing.
-This is probably one for the 'yer dreaming' pile but the integration of some sort of aggregation tool that would essentially automatically backup and allow for presentation in a number of ways all of the content produced by one WPMU install would be great. I started out with Radio back in the day so I'm kinda fond of integrated aggregators too (have to take that into consideration :o)
Although I would say that the major blogging engine that gets the aggregation engine well tied into it could well be the one that does an IE to Bloglines etc! Perhaps...
Um, that's it for the moment I reckon...
And I like / love the invitation forms but do have a mild obsession with forms for people to fill in to get started... so anything that relates to that makes me happy too :o)
Cheers James