Every technology is unproven until it isn't. Hell, wasn't it you who posted a link about Navi in the PS5 thread - and remind me how many games have been played with a Navi GPU yet? I don't think "unproven" is the hill you want to die on here.
Probably the same arguments could have been made for the ethernet port on the original XBox, and they would have been dead wrong. They could have been made about the Kinect, and they'd have been right. One thing MS does know, though, is the Cloud - whether they can make it work for gaming is up for debate but writing it off because you haven't seen it is probably more a function of it being MS than it being unseen.