RPGs infact are the easiest route sans dating sims (i wouldn't really consider this a game, as its a simulator but with brain age who knows what counts as a game nowdays) the only hard part is honestly, the content, sprites tiles animations, everything else is just numbers and simple addition. even enemy actions would be quite easy to do even for things that aren't normaly part of other RPGS, like for instance youre enemies running away.
I've been working with flash for quite a while and it wouldnt be too hard to code something like that at all, but the art is really what count's as a vore themed game that looks groutesque or just plain uninteresting is nothing more than a novelty.