An totally upgradeable console can't be far away now that downloadable content is taking over, can it? They already have various map packs, hardware updates, and even games available on all three systems, so I don't see any limitations to them taking it to the next level.
However, because of the PS3's poor sales it's doubtful that Sony will release another console, but there's still rumors going around about it. It's still another 5-6 years off at least, though.
As far as 360 goes, they've talked about it, and even released some pictures. I really do hope it's not just another Photoshop going around.