I've got a neat idea [sub]That is totally not stolen[/sub]. Take all the starters, and remove their dual-types (Bulbasaur becomes simply Grass as opposed to Grass/Poison etc.). When they evolve through leveling up, they get that dual type. If they don't have a dual-type, give them one. However, if you were to evolve a starter with a stone, like a Water Stone for Mudkip, they still remain that single type but receive a somewhat different moveset as well as different stat bases. Be neat.
And catchable starters would be cool.