I wouldn't consider porn to be lucrative, unless you create the content yourself.. It's one big saturated market, unless you find a micro niche that hasn't been tapped into that much, I wouldn't really bother.
Seconded. I was just asked to project manage a porn affiliate site revamp. They were making $50k+/mo last year, but the niche is so narrow and well, frankly disgusting, that I'm having trouble getting any designer to commit.
Are you looking at designers on the GFY forums (certainly not safe for work for those who aren't familiar with it)? If not look there - they will be used to even the craziest of niches.
In my, ahem, limited experience, it seems like a well-constructed site is very much needed. Most have only the most rudimentary, earlier-this-decade, styles of filtering.
I'm certainly no expert, but the free *Tube sites I've seen are pretty ghetto. Maybe it's better once you start paying, but for instance I'm always seeing stuff I'd rather not in the listings for whatever category. It might be like dating sites, though, where the business model is to keep you on the site irrespective of why you're there, so there's no incentive to make things easy to find.