Bayonetta ain't in a niche genre, it is in the quite popular action genre.
The problem of the 360/PS3 versions of Bayonetta 1: it had much competition of similar games (God of War, Devil May Cry, Dante's Inferno, Metal Gear Rising, Diablo 3) and didn't really stood outfrom the rest... plus a bad PS3-port, which wasn't helping.
If you have a Wii U and want a fast-paced and fun hack'n'slay-game, Bayonetta 2 will be the best option and should focus some sales, which would be spreaded between similar games on other systems.
Including Bayonetta 1 should help... it gives the buyers the good feeling to make a bargain. Nintendo as publisher with their big PR-budget and dedicated fan base should help, too.
1 million units should be no problem in the long run.
