So when's a gimmick no longer a gimmick?
When all the low-budget games quit using it just because it's the "new" thing and the high budget games gets a killer combo of NPD sales numbers and critical across the board acclaim.
In other words, never.
The Wii is a gimmick because it sells systems on a promise. The highest selling games are still Nintendo's first party games. Out of those, Mario Galaxy is not that gimmicky and Smash Brothers fucking uses an actual controller.
Basically, the Wii sells to two demographics: the hardcore Ntards (which are a dying breed in Nintendo's new marketing strategy) and the sheep (general public) who see something new that looks fun and easy to pick up and clings to it. Wii Fit (and other "games" with "Wii" in the title) sells because the sheep want it so they can feel like they are playing games and exercising. Zelda and Mario games sell not because of serious innovation in controls (because there really wasn't any in Twilight Princess) but because the Ntards masturbated over the game and convinced some of their casual friends to play it as well.
About the only Wii game that will actually get third party sales is Monster Hunter Tri, mainly because while it's still a hardcore gamer franchise, it's not exclusively a Nintendo franchise. Again, yet another game you can actually use a controller, utilizing none of the bullshit waggle stuff.
Natal will not be some revolutionary thing that will change the way hardcore gamers play games. In the next year (April 18th to April 18th), Natal releases. In that same year, Microsoft Game Studios has a new highly hyped Halo game releasing with the same sort of hype and marketing schedule Halo 3 had. (beta in the spring, game in the fall.) Also: Gears of War III, which was announced on Jimmy Fallon. Natal isn't targeted toward the hardcore gamer or the 360's core user. It's targeted towards the sheep. Therefore I would expect nothing from it. There's already enough targeted towards the 360's core hardcore user releasing this year. Natal isn't for the hardcore gamer. It's for the sheep.
Hey, at least it has more of chance to succeed. Sony's waggle wand(s) are way too similar to Nintendo's to the uneducated eye meaning the sheep will just think it's a more expensive version of the Wii. It doesn't matter how much more accurate it is.
Personally, I'm still just hoping that Natal and the Move don't catch on. It will just mean that the marketing strategy for every system (not just the Wii) will no longer have me as the target.