There are only 4 teams that would be on there.
USA has 6 competing teams ranked in the top 24 Worlds Standings. (Actually 8, but we are not counting the Shibs or Pogrebinsky & Benoit). If USFSA plays their cards right, it is possible all six could win two spots. Might depend on retirements, but as you implied, there are 4 teams that should be ranked high enough to win 2 non-host spots outright. And two that could get in if 1. enough teams retire, 2. another country chooses to invite one of them, or 3. those teams are invited to Skate America.
Such a scenario, of course, is not guaranteed at all. Last season, the Parsons were ranked high enough that they would have been a logical selection for two non-host spots; but they didn't receive the second invite. There are fewer U.S. teams this season, however. And if Hawayek & Baker travel, then there is room for a second team at Skate America. H&B needed that spot in the past. They were in a very similar situation to the Parsons and McNamara & Carpenter right now. But H&B don't need it this season.
And USA may have teams that do. That's all I'm saying. Maybe it's not a priority. But we are talking about teams that have defeated and/or split placements with the likes of Lauriault & Le Gac, Wang & Liu, Hurtado & Khaliavin, Nazarova & Nikitin, Fournier-Beaudry & Sorenson, Popova & Mozgov, Smart & Diaz, Skoptcova & Aleshin, Lorenz & Polizoakis, Shpilevaya & Smirnov, & Min & Gamelin. It would be a good thing to get those teams out on the Grand Prix, especially considering that there will be limited room in the post season and--particularly if Chock & Bates are really a question mark, healthwise--as there is a possibility that some of those teams could be fighting for a Worlds berth this season.
(For what it's worth, Hawayek & Baker placed higher at SC than SA last season. There's no reason they can't medal off U.S. soil).
Note: Not to ignore them, it is also plausible that a team like Aldridge & Eaton could sneak past one of those top 24 WS teams at Lake Placid and have an argument for SA.
Note 2: Between them, the Parsons, McNamara & Carpenter, and Carreira & Ponomarenko have won 6 Junior World medals and earned 56 JGP dance spots for team USA.