A machine that tickles the subject in it all over.

Idk if I make myself clear, I mean the option of getting/give a blowjob but with teeth froating against the subject's penis, or have an option of just froating your penis/vagina against a subject's teeth until you reach an orgasm 

It's not very a mainstream fetish but as Wikipedia said (lol), it's the second most popular fetish searched on internet.

It could be cool to add to characters an navel and to play with it during sex session, such as fingering, licking it, tickling it, rubbing the cock on it (so hey) and cumming. If the character has this fetish, the anticipation goes higher and gets more aroused and asks to continue if it feels good, or to stop if it hurts and don't like that.. It could be possible to use "toys" such as pen, needle, wax or something like that for increasing the experience.

The navel can be an outie or an innie and the experience could be different according to the navel's type.

Because why not? Strap a dildo to it and you're ready to go...

why not allow general inflation, with a naughty twist? Ex. full body helium inflation (including genitals) and make them your "personal" sex balloon?  

Things like milkers, auto dildos, electro stimulation, portals, tickle machines? Milkers could be used to give pleasure to the subject or your character. Auto dildos for fucking. Etc.

I have a fetish for balls. Sue me. Anyways, the ability to put a subject's pair of balls in your mouth, and gargle/slosh them around in your mouth. The way Fek makes (almost) everything jiggly, it'd be pretty hot.