Yesterday the 'Gaurdians of the Galaxy' were introduced into the animated Avengers Universe through the classic 'Michael Korvac' story. It was a good choice of threat to introduce the cosmic end of Marvel Comics to the TV series. I understand there is much interest in a 'Gaurdians' movie to tie in with the sequel to the 'Avengers'.
Thanos is expected to be the villain in the 'Avengers' sequel so the connections to the Gaurdians make sense. Thanos has been the main villain in that part of the Marvel Universe. If you want to up the threat level you can't do better than Thanos, a immensely powerful and insane alien who worships Death, and his Infinity Gauntlet - a space gem powered super glove that allows it's wearer to alter reality (among other things). I would love to have my own replica gauntlet but like me it would have to light up while I am wearing it.