For me, they're mostly missing privacy. That is, they're not securable from supposedly trusted providers. So for me, a precondition would be full control of the baseband, and running open-source software. Or maybe for now, using Android kernel to load Debian, and nuking the radio.

I'm sure that lots of cool distributed computing stuff is doable. But I'm not much interested until it's securable.

For those who think I'm crazy, consider what company would accept smartphone-like security for its servers. And OK, upon reflection, some apparently do. But my point stands.