I'm pretty sure Saul didn't own *all* rights, just exactly what it said in the article: merchandise, live events, certain film and TV rights for LOTR and the Hobbit, plus matching rights for The Silmarillion and other materials. The article specifically said that the Tolkien Estate retained rights for TV shows based on LOTR of 8 episodes or less, hence how Amazon was able to go directly to the Tolkien estate and secure the rights without cutting Saul in.
The Tolkien estate presumably retains theme park rights and would need to be negotiated with if we want to see Middle Earth in EU.
Which, if that's the case, Uni would be back to having to negotiate with the Tolkein estate for the theme park rights and whoever ends up with the LOTR tv/movie rights and/or WB to use the movie stylings in the parks. Hell maybe Amazon too if the new series is popular enough and they want to use that material. Depending on who buys saul's rights, you could easily have three different TV/Movie presentations of the material owned by 3 different media companies with the Tolkein estate still owning whatever they own. No wonder this has never made it to the parks.