I don't think this should be applicable. Some other players may be impersonated that way and certain Mobs and Player disguises might cause the donator to have an advantage. E.g. even for non-pvp servers, if some are doing hide and seek, etc. , Enderman disguise might cause some other players (at night) to not be able to see the player, though I agree it is fun
This has actually been added before, I was a Sponsor and had /d cow and I think /d pig? It was really cool, but I think they removed it because it got outdated. But it has recently been updated to 1.8. Now I am a Titan, I would really like to see what I could get! Support.