I didn't see the need to re-use Khan, would the film really have been much different it Harrison was just another gentically enhanced superman who like Khan lef/was banished into space following the eugenics war?
Yeah, it would. People would be complaining about ripping off Khan and wondering why they didn't use him instead of another lame ass expy of Khan.
Also I on a personal note would probably not care as much about this character as he would again be just a lame ass expy of Khan.
I wouldn't mind Eve appearing in the next film, but I think the next one should try to be it's own creature. I'm not saying don't have any callbacks to TOS but keep them to a minimum and somewhat in the background than upfront.
Kind of hard to do that in a film about Kirk and Spock seeing as they were the main characters of TOS, not to mention using the Enterprise which was the ship from TOS, as well as the rest of the cast from TOS.