I see the N900 owners more likely to go:
Jolla (if any good) > Android 4+ > BBX ~ iOS 6 > WP8.

I mean iOS and WP are on equal footing if you think about software restrictions etc etc, but at least iOS has a large ecosystem to boot.

QNX/BlackBerry10 seems like the "spiritual successor" to Harmattan and webOS so users are more likely to jump to it than iOS, however it also has some restrictions and basically no ecosystem. Hence, overall a tie with Apple's latest and greatest.

Android 4+ is already has some familiarity with Maemo's backbone. The fact that its the world leader and getting better and better means the majority would rather this than any of the alternatives. Oh, and there's some info/evidence floating around that the next Android version (5.0) will have a dramatic change "under the hood" and it'll rely on The Linux Kernel or a new kernel that shares very identicle resemblance to the mainline kernel (un-forking).

I only put Jolla in the list because I'm hopeful, it may be vaporware afterall. Or worse, humiliating.

(PS What ever happened to the Vivaldi Tablet ?)