It's not in trouble of collapsing, there hasn't been anything worthwhile on the system since NSMB:Wii.
Which exactly is why the Wii is in trouble. It looks like the efforts of third parties to slow down and eventually stop Nintendo are finally starting to pay off. Mainly due to Nintendo's own mistakes though, by failing to have a good holiday lineup in 2008 which has been hurting the Wii a lot ever since.
The Wii momentum collapsed during 2009 and Wii Sports Resort, a price cut and NSMB Wii merely stopped the Wii from falling even further. The momentum had stabilized for a while, but now it looks like it's going down again in the near future.