I have always been a fan of the MOBA style games starting from playing DOTA during my junior high days and I currently play League of Legends. I would love to see these type of games ported to mobile devices with the same multiplayer matchmaking system. The interface and controls for this type of game needs to be carefully designed as to allow the player to feel that they are in control. Nothing destroys a game like having clunky controls. I think Maya has done a good job in bringing the MOBA to mobile devices in their game Legendary Heroes. They still haven't completed the online play feature, but I do see a promising future in this game.
There are a lot of things that can go wrong when making a game like this multiplayer. Any server instabilities can cause players games to crash and a bunch of angry players is never a good thing. The need for a large stable server is probably why there have not been any big MOBAs on mobile devices. I have had some bad experiences while playing League of Legends where my entire game was ruined because of some server crash. Overall I think developing a MOBA for mobile devices is a great idea and I look forward to playing some in the future.