I think three might be too many, but it could work. Although I would agree that it changes a lot about the game, you have to realize that it is that rigid story line that's created all the problems as far as non-legit and botting go. The game became one big item quest, not the dark gothic, co-operative effort it was designed to be. I think having two separate games and better servers that would be Pay-to-play would really get the people that loved Diablo for what it should be, not for what it became. If the story line became more open, it would create less of a feeling for the need to hack to compesate for having finished the game fifty times.
Although it would be a sort of take off from an already poplar idea, I think it would behoove Blizz to cosider following suit with the game(s) City of Heros and City of Villians. According to most D3 'fortune tellers' the game will feature a sort of Heaven vs. Hell idea. What better way of incorporating everyone's preference than to have two different games that operate seamlessly together on the same servers. Have the characters from each customizeable and have the ability to make each game stand on its own as well as interact with the other. The only negative aspect I could forsee would be the limited ability to create a rigid story line, such as in D1 and D2. However, I think it's time that us loyal Diablo players be able to break out of our shell and have the opportunity to become more involved with the RPing aspect of the Diablo genre and less involved with finding the quickest/easiest way to dominate a putrid PK game. Thoughts? Criticism? Praise?