Just for clarification (and they may still announce higher numbers than these, because announced numbers are usually bunk), but in speaking with NYCFC reps, they plan to cap the stadium's capacity at all future games at either 27K or 28K (I forget which figure specifically).
So, people shouldn't be disappointed if they don't hear numbers exceeding like 30K. The stadium's capacity (for NYCFC games at least) is preset at no higher than ~27K/~28K... so figures in that area would constitute a sellout.
They said if demand gets really high for when the Red Bulls come they may consider opening up more sections, but that it would be a very hard sell to management because of the high cost of doing so. Same thing for if the team makes the playoffs, but if they make the playoffs it would be a bit more likely to open up higher sections.
Who knows... if the stadium regularly fills up to that capacity over the summer, they may rethink their plans down the road... but that will likely take a lot of sellouts. Hopefully that happens and the demand greatly exceeds their expectations, but I guess we'll have to wait and see on that.