If the Wii was in HD.

[Kenny]

Here's what I think would have happened, were the Wii in HD:

1) Cost of development would inevitably be higher
2) Cost of hardware would inevitably be higher, hampering the userbase growth rate
3) Third parties would have looked at the Wii HD and motion control, and scoffed at the HD-level development costs plus the uncertainty of the new control scheme
4) Third parties would have written off the Wii HD before the generation started based on the GameCube's performance
5) Depending on whether the higher hardware cost was enough to shoot down the Wii HD, if/when the Wii HD's uptake catches third parties off guard, they'll continue to refuse development for the Wii HD, citing the tremendous uncertainty of a motion-based control scheme, and the need to ensure stable revenue by staying in familiar territory

Which is to say, in all likelihood, %*&$ all would have changed, even if the Wii HD sold just as well as the Wii (and that's a best case scenario).