A derelict spaceship can serve as a megadungeon, too; just think of the scavenging scene in The Force Awakens.
Likewise any of the "distress signal leads to seemingly abandoned ship drifting in space" stories or films. Those can be two phase dungeons, getting in to find out what happened and if anyone (or anything) survived, then escaping from whatever terrible presence is on the ship.
Some glorious Magnetic Rose type shenanigans to be sure.
Consider the following: Perception of distance is warped in the absence of a horizon and reliable reference points. 2 ships 100+ miles apart may appear closer than a car at the other end of your driveway
A Kingmaker game went REALLY off the rails a few years back, and we wound up hopping around the solar system with mythic tiers. We even met Aroden, who in my GM's mind has been hiding out all Ben Kenobi style in some Akitonian cave. As with all galactic sandbox games, it ended when the Wizard accidentally dropped a 15 kiloton uranium bomb on us. Good times.
I find this to be an odd business move considering:
*Lisa is the one who pointed out part of TSR's downfall was due to self-competition with different campaign settings
*Paizo's reluctance to reprint old APs as that would mean competing against current APs
I hope this doesn't come back to bite Paizo in the behind.
TSR had more than 10 completely independent campaign settings running simultaneously. With Golarion as the centerpiece, this feels like a massive extension of the existing CS, though your mileage may vary.
Still, 2 settings over two semi independent games is hardly comparable to TSR's situation. Really the only marketing danger is if WotC decides to relaunch Spelljammer in that window. Which I somehow doubt.