But it's all about software sales, and Vita has shown that it can sell niche games very well. I would list some games that have been 3DS+Vita multiplats and done much better on Vita but there is probably a bigger expert than me out there for that.
Multiplats are multiplats. This is an exclusive game.
Etrian Odyssey IV, the first Etrian Odyssey game released on 3DS (so there was no established fanbase on the console at the time of release) has sold about 250k globally. This is more sales than all but 17 Vita games, and I would call hardly any of those "niche."
There are very few Vita/3DS multiplats to begin with, and those that exist have performed terribly even between the two consoles combined. I can't think of a single exception to this rule. Time Travelers? Zero Escape? The nichest of the niche. Fewer than 100k sales combined for the former, though we have no numbers for the latter.