I don't think anybody would at this point. Sony got lucky in that Nintendo and Sega were imploding on themselves at the time. Microsoft came in when Sega was on their way out, and MS primarily tapped into a US market that was primed for PC-like console gaming. Not sure what a new challenger would bring to the table to be honest. I guess it depends on who went out. If Nintendo bowed out, I'm not sure that anyone tries to fill that void since Nintendo's niche would have been exactly what killed them. If Sony went out I would expect one of two things: Nintendo, being Japanese, releases a traditional console to fill the void. Some large Japanese electronics company releases a console to fill the void. Regardless, if Sony went out someone would pretty much have a free pass at the Japanese market since they don't have interest in Microsoft. If Microsoft went out I don't really see anyone bothering to try and replace them. They no longer seem to be filling a market need that can't be easily consumed by their competition.