A part of the question why my guesstimate is that Ning will be outcompeted by e. g. the lovely Buddypress Community, a sub-community to overall Wordpress Community, in the end.
I tried to get my accounts merged at Ning, since I have some networks signed up with email anders at slice dot nu and ning at slice dot nu, when I was accepting invites, respectively - so my Ning World got basically scattered into two separated parts of that part of the virtual universe.
I used to sign up with [service name]@slice.nu in the 1st wave of the Web 2.0 from 2005 and onwards, with all new services coming up and sandboxed, before I rethought and used only anders at slice dot nu inherently coming out of the learning box as a result of all services going “social” - and my email ID / friend identifier needed to be (re)set to one, and one only. Now done, finally, today, some moment ago, at PBWorks, former PBWiki, flawlessly, in a snap, vs. Not possible, and TOTALLY IGNORED as a prioritized issue with Ning - F U, NING!
TechSmith | Screencast.com, online video sharing, PBWorksMergedAccountsSliceNu