The US skaters must skate good SPs so that they can skate in the later LP groups, who tend to earn higher marks simply on advantageous skate order. The Canadians, two of the Russians, Satoko, and Caro are very good SP skaters so it's conceivable that no Americans could be in the last group for the LP. I think a big reason why Karen gets held back internationally is because she takes herself out of contention after the short and isn't viewed as a top contender.
This comment got me thinking, so I took a look at the SBs for the short program.
1 79.21 Evgenia MEDVEDEVA RUS
2 75.54 Kaetlyn OSMOND CAN
3 74.64 Satoko MIYAHARA JPN
4 74.39 Anna POGORILAYA RUS
5 73.40 Mirai NAGASU USA
6 72.70 Gabrielle DALEMAN CAN
7 72.40 Carolina KOSTNER ITA
8 72.17 Maria SOTSKOVA RUS
9 71.93 Elena RADIONOVA RUS
10 70.92 Alina ZAGITOVA RUS
Mirai's score came at the Autumn Classic, not a GP and Radionova's came in Russia (since I know some people like to look at that).
Taking out the skaters who won't be at worlds, you get:
1 79.21 Evgenia MEDVEDEVA RUS
2 75.54 Kaetlyn OSMOND CAN
3 74.64 Satoko MIYAHARA JPN
4 74.39 Anna POGORILAYA RUS
5 72.70 Gabrielle DALEMAN CAN
6 72.40 Carolina KOSTNER ITA
7 72.17 Maria SOTSKOVA RUS
8 69.50 Ashley WAGNER USA (11th on the original list)
9 68.48 Mai MIHARA JPN (14th)
10 66.87 Elizabet TURSYNBAEVA KAZ (16th)
Ashley's score came at SA, which is not me saying she didn't deserve it.
Mariah is 38th on the list without removing skaters who won't be at worlds. If I counted right, 23 girls ahead of her on SP scores won't be at Worlds, which would make her score 15th. Karen's score is 50th without taking anyone off, and I counted another 9 between her and Mariah who won't go, making her score 18th. I'm not saying this is how things will turn out, but I was interested since groups for the LP were being discussed.
Yes it is.

The reason that it is a bad idea is this: The USFSA tells the skaters at the beginning of the season, "If you accomplish A, B, C, and D, then you will be sent to Worlds."
Three skaters do so. Then the USFSA says, "Oh wait a minute, did I forget to mention E? ... Unless you are Ashley Wagner, in that case you don't have to do E after all."
U.S. Nationals used to be a skate-off among all competitors for worlds spots. Now the proposal seems to be, "If the right skaters win the skate-off, then they g to Worlds. But if the wrong skaters win the skate-off, then we will have a, er, um, skate-off to see who gets to go." I presume that if the wrong skater wins 4 continents, then they will squeeze ia state-off betwee 4 continents and worlds to decide who really, really, really gets to go to Worlds.
Then after that final skate-off, the head of the federation gets to decide which skater he likes the best, never mind the results of all those skate-offs. "Don't like my whimsical choice? Sue me."
Yes, this how it is done in other countries. We should do better. (IMHO

)
I think it would be fine to say at the beginning of the season that results at 4CC can be taken into account when the decision is unclear (obviously this is irrelevant for next season though). Hypothetical situation: There are three spots. the champion at Nats had a decent season internationally and the second place lady had a strong season and is an obvious pick. The third and fourth place ladies had very close national scores and fairly comparable results leading up to Nats. In a case like that, having a final skate off at 4CC could make sense, provided that was established ahead of time. I don't think the team will or should be changed this year though.