It's the people that don't care about graphics keeping the PS2 alive. The Wii seems like most likely to satisfy these people as it has the most games that cater to that audience.
The people who want graphically intense games will be the first to jump ship once something better comes along.
Anyone can guess. It takes no effort to throw out lots of predictions and have some of them be correct. You are not and wiser or better for having your guesses be right. Even a blind man can hit the bullseye.