PC is way more of a viable console replacement than ever before, steam big picture and SteamOS may push it further.
Amazon is dabbling more and more in gaming, buying up studios, they even sell a full blown console-style controller for the fireTV. Apple has yet to fully embrace TV gaming but considering that they care enough to develop a low level API for iOS, that's not out of the question.
Sony and MS are also dabbling in streaming, which takes the console completely out of the picture. And nintendo can always surprise us.
Remember, there was a time when nintendo and Sega ruled gaming, and Sony and MS weren't even in the picture. And they're already showing signs of slipping - the biggest games in the world aren't cod and madden....it's league of legends, minecraft and angry birds. Japan apparently doesn't give a damn about consoles anymore, and we might be next. I wouldn't presume things will play out exactly like they did in the past, so much has changed.