To be honest, this is a horrid move by Nokia.

Why develop a new ecosystem for something that quite obviously will not get supported. Here's what I think Nokia should've done; start with a superphone then trim things down.

In fact trim it down back to a smartphone, and trim down the costs and pricing. Doing things like reducing its quality (physical and parts), reducing its specs, and removing some luxury features. Not to go extreme, but just right enough so that still functions “okay” so that people could still purchase software/content from your App Store and make additional profit.

For example;
SoC (1GHz A8, 512MB RAM, 4GB NAND)
Screen (3.3 inch, 640 × 360, LCD, 2-finger Capacitive)
Features (3G, Wifi bgn, microUSB, mic, earpiece-loudspeaker)
Battery (Removable 1,400mAh)
Thickness <14mm
$99 unlocked (with about half as profits)

Now for the OS go with Android 4.0.3 (higher is better, but this would suffice).
Otherwise, go with MeeGo (with full Qt ecosystem).
If Nokia are contractually unable to go with that route, then go with Windows Phone 8 (or higher).

-And one direction they could take is to alter the OS, ie add their own skin.
Just like how many companies do to Android (TizzBird, Kindle Fire, Nook, MIUI, PAC ROM), Nokia should add their own GUI/UX (Swipe UI and icons) to the latest Windows Phone version.
That way the average consumer would welcome it, not knowing it is WP8, as long as its new, fresh, intuitive and has Apps (Windows Phone has about 100,000 at the moment).