The pretty obvious reason for people wanting this game is its controls.
But i don't think this game is intented to be a system seller, it most likely tries to take advantage of the existing market on the Wii that is badly catered at the moment. It's just a Wii game for Wii owners, nothing more. So in that sense, the question in the OP is rather ridiculous.
Considering FPS is a genre that is being driven forward by the visual performance of the game, Conduit is going for an uphill battle because of Wiis relatively limited visual abilities, but consider the sales of other games alike on Wii, i think expecting sales of one million lifetime is pretty fair. If the game delivers, two million sales aren't out of reach.
There's also few things that need to be taken into consideration; The Conduit was originally started because HVS had already a tech for it, that would be obsolete otherwise. The engine behind The Conduit, Quantum 3, is propably hoped to get into distribution (when Conduit is supposed show what the engine can do, it's the same thing as it is with Unreal Tournament, a tech demo in its basis). The devs have taken the way of fixing the issues they see in other shooters, but this may turn out to be negative just as well, since too much options and "too perfectected" may be "too much" for the market. Of course, what HVS have done, looks promising, but how it turns out in practice is a different matter.