Hmm... Well, if it's in your comfort zone, how about some hypnosis and transformation themed YCHs? As for adopts, maybe branch out some with thinks like ball jointed or plush dolls? Not the small, toy like ones, mind you, but say, a anthro elephant who is a living plushie, privates and all.

There's a lack of good throuples YCHs around, IMO

Honestly I love just regular 'ole solo character YCHs! Often I want art from an artist because I love their style, not because I have a specific idea for a pose, bg, etc in mind. So I love seeing nice solo YCHs from artists I enjoy because I don't have to worry about planning the piece then!

I really love YCH's that have a background and general mood/theme to them as well, since I struggle with those things in my own art! :) I typically prefer happy or nuetral themes to moody/dramatic ones. ( So like... "in a field having a picnic" or "posing on a moon in the night sky" or "waking up from bed" etc <3 )