Man tough question. This depends on so many factors. But if PS3 continues to not sale and continues to cost Sony billions then PS4 will be the first console out and PS3 will be shut down. There is a very strong possibility that PS3 will die before PS2. But here's how it'll work if this is the case. PS3 will go into 2008 still saling how do I say pathetically. Sony will soon attempt to drop price to hopefully entise gamers but over this time they had lost most of their exclusives and dev support and it wasn't going to matter anyways. Now they have a console losing even more money. But this time they could have lost upwards to $4 billion if not higher. Thus if it doesn't start to sale Sony will soon have to discontinue the product and admit a failure. Now the reason Sony would have to do this and not MS like last generation and this is because Sony is just not as big of a corporation as MS. Sony expects to make profits off their Playstation brand. And with PSP a failure if PS3 falls similar ways, we could see a cheaper version of the PS3 on both Sony and consumer by as early as 2009. And we could see a PS4 as early as 2010 to 2011. We'd see them take a similar approach to what the X360 did. Now if MS comes in last there are some pretty strong chances they'll be gone which would leave just Sony and NIntendo for the 8th generation. They'd probably release around the exact same time in 2011-2012 timeframe. If Nintendo lost then I'd expect them to start off early as well but along with MS too as if NIntendo loses Sony is going to win. There is nothing MS can do right now to prevent Sony from winning. It's in Sony's and NIntendo's hands really. Now if Nintendo wins by a landslide some think Nintendo will let out an entire new console, N6, to replace the Wii with more powerful hardware plus an even more innovative controller. Some are thinking as early as 2009-2010. Now Wii would have power to control this if it gained in these 3 years upwards of 60 million buyers. But I don't see NIntendo playing it like that if htye are still making money and saling systems. My best bet is Nintendo has some things up their sleeves to make the Wii very long term. But we'll see. But that's my guesses.
