In any match that matters and/or would be a big draw, they are almost certainly going to go with metlife stadium and its 80k+ seating so as to milk the most money out of the match. Like RBA, we wouldn't be in consideration either with a 40k stadium.
Depends on what you define as a match that matters. If you are talking about world cup games or Copa america or Concacaf knock out rounds then yes metlife will get them. But if you are just looking to make money, we could poach a number of games from a variety of venues in the area. A number of games have been played in a half full Metlife because RBA was slightly too small. Teams are so desperate to play friendlies in NYC proper they have been shoehorning stuff into baseball stadiums long before NYCFC.
Only looking back to 2013 had our hypothetical stadium existed we probably would have gotten a large share of the following:
Hosted by RBA (attendance):
2013 - Concacaf gold cup group stage 2 games (18k, 20k)
2013 - USWNT vs South Korea (19k)
2013 - USMNT vs Turkey (26K)
2014 - Bayern vs. Guadalajara (25k)
2015 - USWNT vs South Korea (26.4k)
2015 - Brazil vs Costa Rica (19.6K)
2015 - Colombia vs. Peru (24.8K)
2015- USMNT vs Costa Rica (25K)
Yankee Stadium
2013 - MCFC vs Chelsea (39k)
2013 - Spain vs Ireland (39k)
2014 - Liverpool vs MCFC (49K)
Citi Field
Israel vs Hondurous (26k)