Using a Japanese survey as "evidence" here is kind of misleading, considering how Star Fox has always being more popular in the West than in Japan... It also doesn't tell us much about its potential audience, just that it's less popular than other Nintendo franchises.
I think the numbers for Star Fox 64 3D show that there's still interest in the franchise, enough for a new game to be a million seller if done right. I agree that balancing expectations and budget here is tricky, but I think it's doable. A good multiplayer mode often compensates for a short single player campaign nowadays, and the budget (and/or price) can be adjusted accordingly. If Sin and Punishment could pull it off on Wii, I don't see why Star Fox can't make it on WiiU. Bigger development costs, but a more popular IP.
If not, they could just make it for 3DS, or as oniyide mentioned, an e-shop release on a smaller budget. Branching-out to other genres defies the point of making one, at least to me. Other IPs can justify experimentation because they're not replacements for the main games, and/or because the characters are popular enough to sell them, and/or they're flexible enough to branch out. Star Fox doesn't qualify in at least 2 of these, and to make something like Star Fox Adventures you don't really need Star Fox...
