I hope it will never happen. As a consumer, I regret that I can't buy only one console and not have to worry about anything else.
Then I remember that the alternative to consoles is PC's. Because a rig costing twice as much, getting outdated in half the time, and coming with a lot of glitches because software isn't optimized for hardware is totally consumer friendly. A one console market will be price and quality gouged, perhaps not to that extent, but a good deal. There is no free lunch.
I think that three or four manufacturers is about right. Some gamers will want to buy multiple consoles, so manufactuerers will have to keep their pices down to continue to attract buyers on the fence. There's also room for multiple high and low power console philosophies without too much overlap.
