Dude...there is already a spanking tag. What do you think? No need to force it. Give the developer a chance to get more fans by opening up for more ways.....I don't think you'll pay him so much, that he can only focus on your spanking fetish....
Don't get me wrong...it's ok by me to have a fetish, no matter what kind of. And on the same time, best igames are those, where you can avoid them, if you want to.