The Wii bubble will pop in my opinion.
The only thing is... people are way overexagerating what that means. Eventually a lot of the old people market will decide they won't want new systems. The centers using them for physcial therapy will slow down, or just stop as everyone who will use one for that will already have one... etc.
Eventually people will actually you know, be able to go in stores and purchase a wii if they want one, any time of any day, just like any other videogame system.
However it will still be the market leader when this market pops... because believe it or not... gamers still infact do buy the Wii. Also, a good portion of the expanded market will still stick around.
The Wii isn't a bubble so much as that a small part of it's consumer base is. Which is the case for any product that so hugely popular it becomes a media story.
Considering how the industry seems to be largely momentum based, it seems Nintendo is using this market just how a spaceship uses those outside rockets that give the spaceship a huge lift and then fall away, i'm too lazy too look up what those are called right now.
Though I think Nintendo is extremely shocked at how long those boosters have stayed on and are still performing. So perhaps a large part of that market actually will stick around.