It would be amazing to have the gameplay of SC4, but with updated graphics and online multiplayer (similar to SC2000 Network Edition, but where each player controls a tile and must work cooperatively to succeed), but I don't have much hope for such a thing given EA's current development philosophy.
Cities Skylines and SC2013 both look great with 3D graphics and more detail, but they both have a pretty small limit on the size of your cities.