I think it would be awesome for there to be a 2D side-scrolling MegaMan MMORPG. I could make my own little MegaMan character, use a cool looking arm blaster, use all sorts of cool unique weapons, and so on. It would be awesome.
Also, I'm suprised they haven't made a MMORPG where you play as a mage or wizard or witch and use all sorts of cool spells and be a part of this academy. The MMORPG that's closest to this is Wizard 101.
A Harry Potter MMORPG would indeed be awesome. Wizards101 is actually pretty close and fun but it's a card game so its pretty slow paced ;,,;
As for MegaMan, I'm thinking more of a stage-based MMO (maybe like Grand Chase/ Dungeon Fighter Online) for that one. I remember playing Mega Man X when I was growing up, I must of been that game a 100 times.
And to throw in my MMORPG suggestion -- Magic the Gathering. All the characters are there, the landscapes, the lore, etc.