If nothing else was happening in Epic for the next 5 years, then the permits for the two very large buildings in WWoHP:MoM and Dark Universe would not exist. But they do.
Lost Continent is getting razed to the ground and Mythos is closing next year, which is going to leave a massive nothing hole in the park. There's no way they would be doing that unless its replacement is on the way. As with a lot of theme park projects, it cost money to tear anything down, so they don't demo something this big until its replacement is ready to go.
These aren't some wild rumors with nothing to back them up, they're gonna' be quite busy with construction for a while. It's just like with WDW which has major projects going on right now in three parks.