Thanos was the big bad of the MCU up until Avengers: Endgame, where he was finally defeated by the heroes, both his present self by Thor and his past self by Tony Stark. In any other context, such a decisive demise would mean the end of the Mad Titan in upcoming movies. But this is the MCU, which has made a party trick out of another fan-favorite villain (Loki) coming back from the dead repeatedly, and as fans on Reddit pointed out, Thanos’ present-day ship still exists in the main timeline as a reminder of the big bad.
Considering how fond Marvel is of callbacks and self-referential commentary, it would be unsurprising if we got to see Thanos’ Sanctuary II ship play a role in future storylines. With the number of space-faring heroes that exist in the MCU, we could easily see the Guardians of the Galaxy, Thor or Captain Marvel investigating the vessel, perhaps discovering some new menace aboard the ship, or maybe even a means to bring the Mad Titan back to life.
There are also the Children of Thanos, the army of powerful space warriors devoted to his cause, who are presumably still aboard the ship, and might cause trouble for Earth’s heroes somewhere down the line, now that their master is dead and they have full access to the resources of the Sanctuary II.
As one Reddit user pointed out, it would be a satisfying ending to the Thanos saga to show Gamora and Nebula now in charge of the vessel. Both heroines were raised by the Mad Titan in extremely harsh conditions and grew to resent him, eventually turning on their tyrannical father and fighting against his army in Avengers: Endgame. What better way to bring closure to that arc than to have the two sisters ruling in place of their father, and righting the wrongs that he committed throughout the universe?