Please no evolutions based on low friendship. Do you know how obnoxious it is to lower friendship? You need to either have it faint a large number of times or feed it a bunch of bitter herbs (which probably won't even be available until later in the game and will probably require a large chunk of cash to get all that you need) and then hope that it doesn't gain enough friendship when you try to level it up considering that doing almost anything will raise friendship including walking a participating in battle.

What if it had multiple evolutions based on the trainer's city color..?