Posted on Slashdot this morning:

Activision wants consoles replaced by PCs

Personally, I don't see this happening. The "walled garden" approach lets the game manufacturers keep their development and support costs low--once it works on one XBox/PS/Wii, it works on 'em all. Unless there's a single set-top game PC manufacturer, that benefit goes away as varied hardware configurations come into play. And if there is a single manufacturer? Then all you really have is a 4th console, and yet another "walled garden".