I do wonder whether they'll add paths to the various lands down the lines, likely once the various expansion pads are filled in.
Disneyland was once similar to Epic Universe, in the sense that all the lands were self-contained areas that had to be accessed via the hub. That decision was likely for the purpose of thematic integrity, but Disneyland eventually reversed course and added paths between the lands. Disregarding problems of congestion, I imagine that the lack of access to other lands from each world will be a frequent complaint in the (inevitable) surveys.
Ultimately, I think Universal could still achieve their goal of having complete separation between the different lands if they created portals within the lands to other lands (for example, a pipe in the Donkey Kong area leading towards Universal Monsters). Or, if they wanted to go bonkers, they could put rides in those expansion pads that would fit with the themes of the lands that are being connected.
If they do decide to go bonkers, that could be a neat way of justifying Luigi's Mansion in the plot between SNW and Monsters. Possibly also a way of justifying calling the dueling coaster between Beasts and Dragons "Dueling Dragons"?