When it comes to game resources like this, so long as you place the access point "early" you can always build out what it gets used for later ... up to and including other zones (instanced or not) ... because it's a transportation link. It's [i]supposed to take you somewhere else[/i], but that somewhere else doesn't have to necessarily be developed and ready in time for game launch, it can be deferred until later updates and developments.

Of course, the same holds true for an airport, seaport, road highway, steel wheels on rails, hike and bike trails and anything else that can "lead out of Titan City" in the direction of the outside world (including an offshore rocket launch complex with ferry connection for getting to orbit).

It's the same idea as having "mine access doors" or manhole covers in the streets and sewer pipes with bars on them to restrict access in Paragon City, the Rogue Isles and Nova Praetoria for use as Mission Doors to underground locations (caves, sewers, underground bases, etc.). Those instanced locations could be built out and added to the roster of missions over time, but all you needed in the shared world was a "click location" for an interact that would take the PC "somewhere else" beyond the current zone (just add loading screen). Even if a character doesn't need to use a specific point on the map RIGHT NOW ... they might have use for it later on down the line.

Note that the same notion holds true for "spiritual sidesteps" into horror stories just as easily.

Go into a shrine and Meditate (the interact) ... if you don't have a mission you'll just see the screen fade out and fade back in as Time Passes™ ... but if you do have a mission that can make use of that Mission Door you'll be transported into a Dream Realm instance that the mission takes place in.

Enter a cemetery at night and Pay Your Respects (the interact) at a specific grave marker ... if you don't have the mission you'll just put your hands together to pray ... but if you do have a mission that can make use of that specific Mission Door you'll be transported to an instance of that graveyard and the horror can begin.

Same deal with putting an underground Hyperloop Station into NRD. It then becomes a potential Mission Door location that is then available for later developments and stories.