First, I don't see Nintendo getting out of the console business. They are very smart and design a system to be profitable right out of the gate so they don't have to worry about playing catch up. So even if the Wii hadn't been a monster success, they still would've come out well ahead. If you can be successful at making consoles to make money, you can make a lot of cash. It's big risk, big reward and Nintedo always has taken the risk and gotten the big reward.
However, if they did and started making games for other consoles, it would be a little sad at first since most of my life, there has always been a Nintendo console. I would look on the brightside though and realize that I would need possibly only one console to get all the great Nintendo games and still get some of the other exclusives and other games that haven't been on Nintendo consoles the last few generations. As for quality, I don't think it would go downhill. As long as they learned and mastered the inner workings of the console, they would continue to produce excellent games.
I worry more about when Miyamoto and others behind their great games start to retire. That is more scary because at some point, that will happen. Hopefully they have some new talent capable of the quality we've seen from Nintendo for over 20 years.
I'll come up with something better eventually...
