Universal Studios shouldn't have a Lagoon. Just doesn't make logistical sense. Hopefully they do decide to make a smaller footprint with the lagoon or no lagoon at all at USF.
Lagoon at IOA does separate all of the islands with inlets but it does give it that feel of being in the middle of an adventure. IOA was designed that way. They are not surrounded by water completely, but Suess, Lost Continent, JP, Toon Lagoon, Marvel, Port of Entry all have water separation to some extent.