1. Sid Meier's Civilization: MMORPG
A Civilization based MMORPG where players and guilds can form sovereign societies and battle other nations for control of the world's land and resources while competing with eachother in every sociopolitical aspect that encompasses all of what made the Civilization series so great.
The possibilities are nearly endless and a Civilization based MMORPG could truly revolutionize the way we look at MMORPG's as linear grindfests and transform them into truly amazing and dynamic worlds full of turmoil, politics and subcultures.
2. God of War MMORPG
When it comes to spilling blood and getting it on with the women, Conan can't hold Kratos' jockstrap. Cratos in Mythology and in the game was the son of Zeus. In God of War, the MMORPG, players can align themselves with different Gods and Goddesses and battle it out mercilessly for control of Mythological Greece and beyond. This title would of course be rated M and would put the matured centric hype of Age of Conan to shame.
3. Star Wars MMO
Although it's been done before, it was never done right. To have such a prolific IP go to waste is the biggest shame of the MMORPG industry. There should be 5 million people playing a Star Wars MMORPG. Unfortunately, the task was given to Sony Online Entertainment who has managed to alienate and shun loyal and dedicated Star Wars fanatics when they relaunched their sandbox Star Wars MMORPG as a fixed path FPSish MMORPG with the New Game Enhancements.
It's time for SOE to pass the torch and for LucasArts to realize that if done right, a Star Wars MMORPG can be successful.
4. Mario MMORPG
Why not? Combine all of the past Mario hits and turn it all into one big MMORPG. Allow players to choose between the good and bad sides of the Mario Universe and compete against eachother in fun filled head on minigames, run quests and save (or kidnap) peach.
There really aren't any good family and kid based MMORPG's out there and this would surely topple Toontown and Hello Kitty Online. It could also mean the demise of Habbo Hotel and Club Penguin. Kids are only playing those games because there's nothing else to play. Give them something good to sink their teeth into and $$$$ all around for Nintendo.
5. Spore MMORPG
Spore is intriguingly interesting. The concept is so close to being an MMORPG the way you will be able to send your creations to others and see what happens. If you take that process one step further where there were huge persistent worlds where players controlled local ecosystems and used their creations to invade other ecosystems in a global game of survival of the fittest.
What are your top 5 existing IP's that you would like to see turned into an MMORPG?