Well, I guess Guardians it is. Just to put this out there, I really liked the movie but I really wonder how they'll make it fit. I have hope but it seems like a stretch. RRC is definitely best place to put GOTG because it probably is better fit than current ride with the direction DHS is going now.
As for IP in Epcot, compromise is key. Frozen in Norway does not fit well and is a fantasy world within WS. In contrast, things that take place in the country and better yet show culture of said country should work well (Coco, Rat, Mary Poppins?). Of course, this assumes ride/attraction is done well.
In Future World, Nemo is a good example of one that could have been done right. Either make Nemo more subtle like Turtle Talk was at first and just a part of the Living Seas or make a really good ride that doesn't need Nemo to draw crowds but has him anyway. Nemo would probably be more vastly forgiven if the ride was not just a rushed merch-seller. (I don't know how long it took to build, but it just is not that great, especially as the "headliner" of the Seas pavillion.)
Overall, I believe IPs can work in Epcot if they work to communicate the ideas and themes of the park - preferably the current themes IMO. But if Epcot is forced to communicate the IPs' themes and ideas (not to mention make $), that is when the heart and soul of Epcot will officially fade away into history.