Most redis users are running multiple instances regardless. That some of them happen to be on the same machine is largely a detail. It would make a little diff

Most redis users are running multiple instances regardless. That some of them happen to be on the same machine is largely a detail. It would make a little difference if there was a single hot key, but that's a bit unusual. Typically there's some subset of keys that are hot, and you can get them to hash across instances. People also tend to cache those values on the clients, as banging on redis constantly is a waste.