It has so many varied locations now with the Menagerie, Underbelly, Spire of Stars and the rest that with a few more connections and tunnels it would make for one enormous and cool patrol space complete with a NPC vendor (finally add Gus the slovenly) and even unique public events.
Consider.
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Welp, if they made the entirety of Leviathan a patrol space, they'd have to do the same thing with every other location in the game. Not saying that that wouldn't be awesome... but that that would be a crapload of work that they more than likely wouldn't have the server space to do. Earth alone would need its own building to house the server required.