Well, we know from Wii U sales that their dedicated fanbase, the kind you're describing, isn't as large as they would want you to believe. I think the Switch is not only doing well based on Nintendo fans but also the much better marketing compared to Wii U, a Zelda title right off the bat, and that it doubles as a handheld game device. I think you're right, though. Switch is going to need more games and they're going to have to be compelling. I think that as long as Nintendo continues to do things that go against the mainstream market, the only way they won't play second fiddle is with another miracle like the Wii experienced. Though that begs the question, does second fiddle matter when you're still successful?WiiU sales are prabably a decent estimate for the size of their hardcore base. The thing is though, the WiiU sold about 13 million and the Switch is still only on 2.7m, so there's less than a quarter of those people that have bought it. So its mostly successful right now by still selling quickly to WiiU owners, but in a years time almost all of those guys will have a switch and they'll need to pull in new people through strong marketing and a strong games lineup.
It really depends on how well they make games for Switch and push them out. It could easily flop as the mass market rejects it and sell gamecube level or it could go more like triple the gamecube's sales. Only time will tell on that one. Sales for this FY will be a good indicator.