Definately a good dream. BUT aren't you underestimating the fact that hardware developers (like the mentioned galaxy s developer samsung) will not support you with drivers for ther HW or even open up specification so you can write your own ones?
IMHO that is the reason why there has been no really mainstream true linux phone. I remember this barebone phone where a linux was running, but whiche other phone HW is there to use? Nevertheless it has to be on top of the shelve if you really want to attract smartphone enthusiasts like us