If the new owner is more reasonable than the former owners, I could see a lobbying effort down the road to join MLS. It's a no-brainer that MLS is the path to marketing & top competition in the US, so being a smart man that he is, he will not want to be forever in a second rate league as the ugly stepchild to two other teams in NYC; he should have ambitions to step up.
Hell, I think NYC could easily have a third team if located in the 4 boroughs with a stadium (I cannot fathom they will ever have enough support as a fringe suburban LI team). I'm not thrilled about sharing a stadium, but wouldn't say no if it helps grease the wheels (as long as NYCFC owns it). And as much as I hate the Kosmos, I'd love playing them 2-3 times a year - that would become the ultimate derby in the league, and from a TV perspective, that plus the RB derby would always be a ratings bonanza (plus the RB/Kosmos derby).... And TV ratings are how the league will ultimately make its windfall $$ - Garber will definitely change his tune if the new owner is approachable.
But the Kosmos will have to survive the NASL for a few years to make that feasible, so surviving Mount Everest...