1.) A roleplay where I can play a dominant female character without my partner trying to jam in every kink under the sun, and make it as hardcore as possible. I don't even make threads seeking this anymore because I get overwhelmed by responses, and the vast majority want their fetishes to override the plot. Half of them don't even read the thread, they just see "dominant female" and pitch their own ideas, usually involving kinks that I listed as a hard no.
2.) Diversity. Everyone's white and smoking hot, either slim or curvy/muscular, and in perfect mental/physical health. I'm guilty of this too. I don't want my partners to ditch because I'm not playing a character that appeals to them. But honestly, I'd love to play with and to a broader spectrum. But you say "interracial" and people go straight to the fetish. Same thing if you say chubby.
3.) The opportunity to play a submissive character. This is a hard to fulfil craving partly because I'm picky. I won't play submissive female characters, and I want an emotional connection, not just smut. End result, I mostly play dominant males.
I can think of a few more, but these are the ones I've pretty much written off as impossible to make happen.