At the 2017 D23 Expo, Disney officially confirmed that a Guardians of the Galaxy Attraction will replace Ellen's Energy Adventure. Ellen's Energy Adventure will have it's last day of operation on August 13th and then work will begin on the new Guardians of the Galaxy attraction.
Concept art shows that the Universe of Energy building will remain and a Nova Corps ship will be built outside as an icon. Additional characters including Groot and other aliens also appear in the concept art.
As part of the presentation, it was explained that Peter Quill (a.k.a. Star-Lord) visited EPCOT Center as a child and that will tie the attraction to the park.
While no specific date has been given, the attraction is expected to be open by 2021.
Our full Guardians of the Galaxy Attraction Rumor Tracker can be found here.