Interesting idea, but I doubt it would ever happen. US judges go through years of training and moving up the ranks -- sort of like competitive skaters -- before they reach Nationals. They have to judge at regionals, sectionals, pass tests, etc, before moving up to Nationals. I also cannot imagine the ISU or the individual skating federations financing the expense of air travel, hotels, meals, and the like.
The only positive aspect, in my opinion, would be the cessation of the "favoritism" that sometimes is displayed at Nationals. Some of the judges come to Nationals with pre-conceived ideas as to who will make the World Team. Sometimes they are absolutely spot-on with their decisions, while other times, perhaps not. There isn't much opportunity to shake up the ranks among the top five, especially with a skater making his/her/their first appearance at Nationals. It would take someone truly exceptional to come into Nationals the first time and win a medal. There aren't that many Oksana's out there, or at least the judges don't recognize her/him/them.
Carlo Fassi once joked on camera about figure skating judges. (sic) "Your first time out, you can skate great, but because the judges don't know you, you receive lousy scores. The next year, you may not skate as well, but the judges will give you the scores you should have received last year."
"Sports Illustrated" once labeled the Nationals judges "The Todd Squad", as a swipe at the high scores they perpetually awarded Eldredge. Not to diminish Todd's ability, but the judges clearly wanted to send him to Worlds or the Olympics as the US Champion.
Then there was the 1976 US Nationals. Dorothy Hamill skated a "comfortable" long program and eliminated several of her jumps. It was more of an exhibition than a competitive program. Linda Fratianne, as the new kid on the block, landed two triples and finished second. Many thought Linda should have won, as she clearly outskated Dorothy. But the judges wanted to send Hamill to the Olympics as the US champion, as that would give her a better chance to medal.