The ability to attach a device to your subjects that lets you control their bodies while they're conscious, allowing you to make them say and do things involuntarily such as masturbate or have sex, but with visible intention to resist.

Feed test subjects to make their bellies grow. 

Some actions to play or stimulate yourself with a subject's teeth should be a good addition to the game. 

also cum on someone's teeth, that could be beautiful <3

Perhaps include a stethoscope and/or an ekg machine that lets you hear the subject's heart. Their heart would beat faster relative to their arousal, but it would have a reasonable BPM cap to stop things from glitching out and spiraling upwards. Species specific heart rates would be interesting as well (avian species might have faster heart rates. dragons would be slower, etc) but not necessary. I guess this files under general medical fetish, but cardiophilia is a particular aspect of the fetish that deserves extra attention.

Not hard to draw blood though.

Braces fetish is really underated in furry art, the braces gives the girls (and also some boys) a sexier look, and being capable to cum on some character's braces will make your game really inovating, and also you'll atrack more people