From my understanding it's completely different to the way they deal with things compared with golf and putters for example, which is how your post reads in your interpretation of use of the rest in snooker. I can't remember ever hearing of a rest that was deemed illegal, and if there is such a rest invented that is so good you can't miss, I don't think even that would be deemed illegal because well, apart from it being impossible, playing with a rest no matter what shape it is won't be as easy as being able to reach the shot without a rest. I think the examples you mentioned like the hook rest comes up so infrequently that they decided they don't need one.
I did recently (as I was drifting off to sleep) think of a shape of rest to deal with those shots you face down the rail with the white just past the middle pocket close to cushion cutting back the shot. But if what I thought of would make any money it would already exist. I mean if you look back during the whole World Championships with all tables televised, even in an event that big with so many frames played, the shot only came up maybe about 5 times in total. So what's the point in banning such a tool if one is ever invented that makes that shot easier if it's hardly ever used?