Inside Out makes more sense than either Guardians or TRON for an Epcot overlay. IO in the old WoL pavilion and updates for Energy/M:S would do wonders to enhance that side of Future World.
Plus, since Ellen is still well-liked/popular, why not just bring her in to film an updated ride film, add cushioned seats to the RVs (those hard benches make it hard to last 37 minutes
) and overhaul the dinosaur sequence? It would end up being far cheaper than the $200-300 million for two GotG attractions and allow Imagination, M:S, SSE and Seas to get enhancements, too. You could even bring back Bill Nye due to 90s nostalgia.
Of course, TDO doesn't make logical decisions for Epcot... but if Inside Out didn't get a greenlit attraction for Epcot (despite its edutainment potential), I just don't see how GotG or TRON would work.