VF characters are within the same boat as Naotora except she is likely to obtain one. (She even has the I'm A Fighter slogan outfit I believe, which is odd since she's also not part of the DOA universe) She's a Samurai Warriors character from KOEI which Team NINJA is a sub division under them. It's just easier for the character.. whereas characters from SEGA is like a journey to another planet just to ask for permission.
Lately Team NINJA has been making collaboration outfits that is difficult to add to characters that were not originally made by Team NINJA. The biggest chance is outfits they make on their own that doesn't suck or fan made outfits, yet those are once in a blue and resorting to luck in hoping for the best a particular outfit makes it in from fan made ones, which is also a drawback. Basically luck is not on my side if they continue to make more than 50 collaborations a day. (Unless the people who made the collaborations also talk to SEGA about it.)
Besides, I only buy outfits for Akira anyway and very rarely for Jacky (actually, think I bought only 'one' outfit for him). Don't really pay attention to Pai or Sarah, sounds cruel I know.