I wouldn't mind alternate shiny colors, just because some Pokémon have really ugly shiny forms. However, I don't really think anything else needs to be done to a Pokémon's aesthetic appearance to be honest. Actually, other than color alterations, I'm kind of scared of what else GameFreak would come up with for a Pokémon design. Plus, it would take up unnecessary space that could be used for something more useful.
Gen V introduced Hidden Abilities and even though they may not be as rare as finding a shiny or aesthetically different, I think it was a neat change for each Pokémon to have some sort of special ability from what we're used to. More so because a lot of the Hidden Abilities given are very useful.