Instead of a regular milkers which has the subject orgasm and collects it, there could be different variations. For example, a milker with a hole at the top. Sort of like a Fleshlight but the subject will climax onto themselves instead of it being collected.

Be able to grind your penis together with the test subject's.

The option to be able to put the penis in between subjects boobs, there could be like a minimum boob size in order to be able to perform this action

That would be cool.

I really like the idea of musk and a strong smell coming off of someone. Something like the subject being noticeably sweaty, dirty, or something like that. Maybe it could go along with smegma, since I like that too, and it kinda makes sense to pair with being dirty. 

I would love to see some more belly-centric interactions such as navel insertion/stimulation with toys or tongue, rubbing, patting/slapping, kneading/groping on sufficiently fat or inflated characters, and possibly expelling cum (or other fillings if added) with applied pressure.

Growth/shrink ray

Coded preferences for small and large genitalia, ability to make and receive demeaning/praising comments based on genital size, ability to compare your relevant genitals with the test subject and vice versa.

On subjects, in their holes, after oral