Nintendo was super restrictive about demo discs on the Cube. If they weren't willing to follow standard industry conventions when they were getting their ass kicked and were in no position to be trying to force needless restrictions on anyone, why would they suddenly now change their mind? Nintendo plays hardball even when they've have no influence and no power and supporting them is doing them a favour. So now that they actually do have power and can afford to be stubborn dickhead Nintendo every once in a while I expect them to do so. They hate demos, the Wii sells out everywhere, so there's not going to be demos or at least not in a way we expect.
If Nintendo does demos I expect it to be something we can't keep. They like how on the DS the demo disappears when you turn the system off. If we can keep playing the demo for all eternity they think we won't buy the full game.