I second Broran Inc. maybe not the trans, no opinion on that, but the rest i like a lot. although wouldnt be mad if you add trans if thats something you would be ok with adding. 

inflation, mpreg, urethra. all things i like. Also just had to add, since i read another comment. cursed comments like tentacle underwear sounds fun. and oviposition. maybe also the posibility to keep cum or eggs inside even after the sex for a bit, even if not permanent? although no clue how hard that would be but might allow some gameplay features where you need to be inflated to have more mass or stuff like that

also think with krillin he meant more like, make it look like the struggle is two sided ( player tries to get away while others try to fuck him), not sure why since it already works that way anyway. but also like humiliating comments in the end? like, how weak or submissive or slutty the character is to lose to him. etc.

spanking,and more spanking,and spanked to orgasm！

I'd love to see trans male characters (or at least one) aka a 'cuntman'

Also more inflation without pull out, like knotting and staying knotted for a bit.

Would love to see some urethral stuff like tongue in urethra or urethral fucking/cock-fucking.

mpreg is fun but not for everyone and also maybe characters with large balls but not large cocks, like tanukis, normal cock sized for the game but big balls :3

pregnany

Liquid latex would be nice 

I would like to see some facesitting/butt smothering

Chastity and Denial play

Thick cum(Like an orgasm, but the cum gets stuck inside)

Ball growth via a plugged prostate(the kinky kind, not the medical kind)

Size dif,hyper stuff,inflation

ball worshipping, multiple orgasm in one sex scene would be nice.

Might be hard to do, but i always had a thing for cursed items

I'd have to say some more monstrous features or creatures the better.