Considering that last year there were 3 big games and a price cut, and that this year there were no big games and no price cut, I would say momentum has maintained itself fairly well. Even with Microsoft and Sony bursting onto the scene with motion controls and slimmer consoles, Nintendo still won last year when it came to overall sales.
Certainly they will be making efforts to maintain and increase Wii's momentum throughout the year. They will likely have new motion-plus software not limited to Zelda. I think Wii Relax will be released at some point this year and that, like Brain Age and Wii Fit, it's going to push hardware as it attempts to expand the gaming audience.
They also have the option of a price cut which they could do at any point in the year. I believe at a price point of 130-150 dollars sales would start to explode again. They also have the option of different colors and bundles. The red wii bundled with mario was extremely successful and I wouldn't be surprised if they brought it back.
The other option is that they could simply update the Wii hardware in the same way Sony and Microsoft did (not changing the internal specs, but simply changing the look or external functionalities). I don't think this option is very likely, but if it did happen I wouldn't doubt it's ability to boost sales back to astronomical levels.
Lastly, the one positive thing that I think we saw this last holiday season was the stronger sales for third-party games. Nobody has been talking about it, but there were a number of big third party games that did quite well. Companies like Ubisoft and THQ must be having a change of heart towards the Wii, and I think we may see 3rd parties finally start to break down and actually make some good content this year.
So a simple rundown:
1. More motion plus software (Zelda, Wii Sports 3?)
2. Wii Relax and Vitality Sensor
3. Price cut to $130-150.
4. New colors, new bundles. (green with Zelda?)
5. Bring back red mario bundle.
6. Wii hardware update (not graphical)
7. More third party support, hopefully...
