Looks really polished. My one point would be that I would consider making the default model a realistic mannequin (or ecorche if you have it). I get you're saving that for pro, but I think that would make it more obviously appealing for people studying anatomy / perspective (which might be a bigger market than pros looking for pose-reference for illustration work).

Having the abstract mannequin as a default may make people feel like they might as well just buy one of those wooden posing dolls (https://www.amazon.com/wooden-mannequin/s?k=wooden+mannequin).