Biggest problem will be price. As it is, Wiimotes are *still* £30-something even after five years of production, not to mention MotionPlus, Nunchuk, etc.
That was always the biggest barrier to > 2 player gaming on the Wii for me, if I'm honest - you only ever get one with the console and you're usually willing to push to a second if you get it "free" with a decent game, but after that there's little incentive to continue because of the price and even the availability in the early years - they could easily hit £50 for a full set for a single player. And that's not even considering the WiiFit which is basically a one-per-household item, if that, and is still prohibitively expensive even now. You should not be paying almost as much as the price of the console in order to get two players on a par in terms of controllers.
At one point people were hacking the Wiimote to be things like presentation remotes, etc. but when you consider the price of the hardware (including a standalone sensor bar in that case), it's actually just cheaper to buy a presentation remote or a cheap interactive-whiteboard-type sensor that sticks to the wall.
I don't doubt that Nintendo's bulk-buying could bring the price down enormously but they didn't really do much to accelerometer prices in terms of the Wiimote's final price (or even that of it's knock-off rivals). And they'll pull the old trick of only giving you one controller because "you can just hot-seat". That said, Nintendo tend to know what they are doing and will make lots of money off everything through sheer popularity and business sense. But it's annoying that the "console" price never includes two complete controllers any more, and that they push 4-player or more games when hardly anyone can afford that kind of setup without carting equipment round to other people's houses.