Marco's getting a character development arc like Star had. He's going to make mistakes and learn from them.
TransMarco tumblrites are a small echochamber clique on tumblr and no one cares what they think. It's their fault for thinking their headcanon was canon.
I feel like there was potential for an aesop about not living like a bunch of liberal art students, and maybe having SOME structure in your life, but instead, the moral of the story is The Revolution lives on, despite evidence that the Che Guevera legend was built on a lie.
I think Nefcy kept her cheekmark thing vaugue on purpose, just in case she could tie it into some other twist she hadn't yet planned, and now she has it, and it was foreshadowed when Star's cheek hearts were tested for corruption. Heinus will probably get the Ludo treatment, with Eclipsa in the Toffee role. Wild speculation, feel free to pick apart.
It's obvious Marco isn't Lavabo's squire anymore, that was the point. Star could have given him any position she wanted, but didn't want to abuse her power, until Eclipsa convinced her "Why not? You're the princess, who's going to stop you?" So she abused her power a little bit so that she forced Marco to give his wedding vows and be on a leash for the rest of his life.