OK, I'm going to try and give this forum a bit more structure. First, I think we need to outline design goals: just what is the purpose of this game subsystem (which is basically how I'm envisioning it), what do we want to be able to do with/in it, and how can we achieve those goals using existing rules, tweaking/cannibalizing existing rules, or homebrewing from scratch where necessary.
I also definitely want a "brainstorming"/"data collection" thread where people post things that they've experienced in dreams, heard about from the dreams of others, or seen in movies about dreams (Inception, Altered States, Flatliners), so we can adjust our design goals include interesting dream elements that get brought up there. I'm going to go ahead and start those, and maybe move some posts around into them.