Given what Expedition Everest has done to boost attendance at Disney's Animal Kingdom, I can imagine that WDW management would like a roller coaster at Epcot -- the only WDW theme park without a roaster coaster (unless you count Test Track as a roller coaster).
However, the credibility of this particular rumor suffers greatly due to the following paragraph (originally at The Disney Reporter and then quoted at Mouse Extra):
It has not ‘officially’ received the green-light but is considered a shoe-in to do so as Mitsukoshi has offered to put up money, as they have the past few years for the great redos of their department store and dining facilities at EPCOT.
It makes no sense that "Mitsukoshi has offered to put up money" (which would be in the $100 million ballpark for a major immersive thrill attraction). Sponsors pay sponsorship fees to to gain advertising exposure, consumer goodwill, and favorable reputation. Mitsukoshi operates primarily in Japan, with some additional operations in China and Europe. Mitsukoshi only has one retail/restaurant complex in the entire United States -- the Japan pavilion at Epcot.
Why would Mitsukoshi "put up money" for the thrill ride? It just doesn't make sense. Given that the Mitsukoshi funding is an integral part of the rumor at The Disney Reporter, it makes me wonder if their source really has any idea of what's going on.
Would Mitsukoshi's revenue at Japan pavilion at Epcot jump so dramatically that profits would increase even after accounting for the cost of the ride? Would Mitsukoshi gain so much goodwill from the relatively small number of Japanese tourists at Epcot? If Mitsukoshi really wants to sponsor a Disney "E" ticket thrill ride, would WDW really be a better location than the Tokyo
Disneyland resort?
Sure, Mitsukoshi has invested in improvements to their Epcot retail store and restaurants -- but they derive revenue from those operations!
If the rumor had been that a Japan-based, global consumer products company (such as Sony) would be the sponsor, then the story would have seemed more plausible.