I'd like to see a fantasy type line with CoD/Halo articulation. I did pick some of the Warcraft sets due to my love of the fantasy genre, but I think the Warcraft designs are too garish. Something like Skyrim or Dragon Age would be cool. Or even an original, Mega Bloks created line would be cool. My dream would be for MB to license Warhammer, but I think they could also just create their own generic fantasy theme. Maybe even develop a mobile device app game around it to give it media.
MB now has horses available, so mounted troops are possible. Hoods from AC and scarves from CoD could be re-purposed as well as weapons like AC swords, maces, and halberds. Sets could be based around large monsters (dragons, giants, trolls), vehicles (wagons, ships), and buildings (tunnels, inns, campsites, ruins). Teampacks could be either army-builders (orcs, human knights, dwarves w/shorter legs) or parties (ie human knight, dwarf, elf ranger, and wizard).
We have a variety of themes in MB so far, and some more coming out. I think fantasy is a major theme not yet covered with the more collector-oriented articulation.