Some have been established already. Just because "Oh humans in Sonic suck" doesnt mean we cant make them better. "Ew beastiality" we can advoid that. It wouldnt be fair for people who want to introdcuse a charcter of a particualr race (As said by 3K) So yea. Humans should coexist with Mobians. Hey, in the Archie canon, humans are doing pretty well. So why not give them a chance.