Difficult to say, clouded the future consoles of Nintendo, Sony, and MS are.
Nintendo will continue to make consoles until the company dies, which is going to be a long, long time from now.
MS has one more in them I think. So far, they have lost a couple billion dollars in the console market and I really have to question if they are in it to get into gaming or to get into people's living rooms. If their XBL downloads (movies, tv shows, music) don't take off and they continue to be unpopular in Japan and Europe and they aren't making any type of decent profits, I think the company will pull out of the industry.
Sony is a tricky one, but here it goes. Sony is never going to leave the gaming business, however I think they will leave the game console business. I think PS4 is going to blur the line between a game console and a multimedia computer. We are already seeing Sony start this type of thing with offering SACD, Blu-ray, DVD upscaling, Web Browsing with the ability to download Divx, WMV movies, MP3, and photo support and I think PS4 is going to push it even farther away from being able to be called a game console. Yes, the thing will play games, but it will do so much more than that, that you never would even have to play games on it and you could easily justify the purchase.