I'm on the fence about it. As it is written right now, no restriction applies. So you could technically have a rogue who is S class in a skill by level 3 if he dumps all his skillpoints into that skill and nothing else (not something I'd imagine most rogues would be inclined towards doing).
I am thinking that the ranks themselves could be more meaningful if the old limit remained in place though. So at S class you can actually give level 19-20 abilities without worrying about unbalancing the rest of the game.
That sounds good. Making skills more valuable, and able to really scale with level compared with spells, would actually make the skill monkey role valuable. Maybe just slap a restriction on how high your level in skills can go, such as-