They'll shut up as soon as they realize that Nefcy isn't playing 4d chess and that there is no twist. Starco will happen. It'd be bad writing for it not to happen at this point. It not being endgame would kind of make no sense either, unless the blood moon is a curse. I really think you guys are overanalyzing this. What kind of ending would be "Marco ends up marrying a normal girl and Star runs a kingdom by herself", or even worse, with a character that isn't introduced yet. Why would they draw so many parallels between Marco and River then? Why would it make complete sense as well? Moon married outside tradition by marrying a fucking barbarian prince. Star would be taking it a step further, and marrying someone from a different dimension.
Maybe they'll give Star another love interest and finally cuck Marco. That might happen actually. Only time will tell.
All I know is that without retconning a bunch of stuff, I don't see Star and Marco not ending up together.
They need a way to stall Starco. That's either going to be with more conflict, or either one of them having a heel turn, or they're actually not going to stall it.