Could this be a potential new niche? or would it generate no interest?

[KG Gary]

I think some porn preferences revolve around what you don't/can't have in real life.
For example a guy with a lovely partner who would rather stick a needle in her eye than go near his cum might have a thing for watching women who genuinely appear to love cum.
Maybe the whole swallowing thing is more to do with the woman really wanting that cum - to not make the guy feel like he's a repulsive cream-shooting freak.

I've always found that the biggest turn on in real life, and the biggest by a long long way, is a woman who wants to have sex and enjoys being forward and taking the lead. So I'd definately agree that happily swallowing rather than a facial or dribbling or whatever, even if you never actually see any gloopy stuff, could be a real winner providing that the gal isn't gagging as she swallows - she has to love doing it or at least convincingly appear to love doing it.