It's not surprising having junior teams shift. It is surprising having a bunch of junior teams at Wheaton shift, and two of them on the Junior World team. It takes a long time to get there. Starting over very often means forfeiting ground. Maybe you gain an extra junior season or two, but that's no guarantee you ever get back on that JW team. (While you could very well have a crack at Challengers and/or Skate America in seniors if you stick it out with your partner. And there are no audiences on the JGP so why not go do Challengers with no audience?) It's not often that starting over gets you an extra season or two at the top of the National field.
I suppose for a skater like Somerville, it's more likely to earn a medal on the JGP (some time in his next 3 seasons) than it would be to earn a medal at a Challenger.
If I was going to estimate--based on all the junior & senior teams that we know have split or retired since last season, many of them not from Wheaton (DelCamp & Gart, Haines & Koszuta, Efimova & Petrov, Wolfkostin & Zhao, the Purnells, Manta & Johnson, possibly the Elders?, Weatherby & Bogomol, Pettersson & Carey, . . . and many from Wheaton (the Parsons, Gropman & Somerville, Gunter & Wein, Amoia & Becker, and probably the Greens), I'd estimate 1 new team gains ground on where both individuals were last season--especially internationally. And the lower you were last season, the better your odds of that because you have less distance to fall and so many other teams have kindly split up to help you gain that ground.
If there has to be splitting, it's actually good that so many teams split because better matches may be the result.
Who is this likely to be good for? Russia & Canada.
Several of these teams weren't going to have any immediate impact on Canada or Russia.
-Haines/Koszuta and Efimova/Petrov were aging out of JGP and wouldn't have an immediate impact (if ever) in Sr. with the deep American field above them.
-The Purnells, DelCamp/Gart, and Amoia/Becker, weren't at the international competitive standard.
-Gropman/Somerville could have contended on the JGP next season. Gunter/Wein were around a top 6-8 JGP international team so it would depend on how much progress they had made and the depth of the field whether they could medal.
-Wolfkostin/Zhao had a lot of potential, but breaking up at their ages is fine and they have plenty of time to build momentum.
-The Greens were a real medal threat, but Wheaton's track record with sibling teams may have given the Greens pause. The Phams disappeared as novices. The Beckers were amazing technicians who won the low-level titles and then became a size mismatch. The Parsons did amazingly well through juniors and also succeeded in senior (a GP medal is nothing to sniff at), but their size mismatch also did them in. Maybe the Greens saw the writing on the wall for their future, and decided to break up now rather than do very well in juniors but not reach their ultimate senior goals.
Canada is positioned well for the next JGP with several middle-jr.-aged teams who aren't so young that they just look cute and who also have a couple more seasons to establish themselves, e.g., Bronsard/Bouaragui, D'Alessandro/Waddell. Russia will be just fine with Ushakova/Nekrasov, Ivanenko/Karpov, Shanaeva/Narzhnyy, etc. But IMO, they were positioned well before all the American splits.