Awesome, go get 'em. I think you'll have some stiff competition from BuddyPress, particularly since they've got a head start on the extensible platform, but I wish you guys the best... it's anybody's game at this point. Ning is really the platform to beat, in my opinion at least.
That's part of the plan. Remember, WordPress wasn't born with plugins and hooks; it grew them.
"Release early, release often", right? This is the "early" part. :-)