That's a great idea! That way you'd have the worst of possibilities: software upgrade hell all around ("company X is not upgrading the OS Y on devices Z and W anymore"), hyper-confused buyers (most consumers can't even insert a sim-card without help, let alone pick an OS) and an all-around tendency to nightmarish support experiences ("we don't fix X phones if you install Y on them!")

That would be a huge step back from a consumer perspective, IMHO. The "mobile revolution" is in full effect because the devices have got SIMPLER, not "more open". But I'm sure Stallman and others of his kind would LOVE it...

edit: removed "neckbeards" reference that could sound offensive to more zealous uber-nerds.