I'd like it. I don't know all of what I'd use it on, though. Maybe Gardevoir being female-only, except if she was caught or transferred that way. Same thing with a couple others similar to that. Other than that I don't really know what I'd use it for but I'd definitely like it better, makes them sort of follow the intended stipulations put in place in the pokedex and also in the show (from the one episode I remember of Slowpoke's evolution).
Also I would create a slow-whatever evolution with Cloyster being required.
"The point of war is not to die for your country. It's to make the enemy die for his."