It would have been a guaranteed spot at all of the championships, and, presumably, permission to attend any internationals they were willing to fund themselves.
Early in their career, US first and second were a lock with Belbin/Agosto and Davis/White, they were always behind Davis/White and Virtue/Moir at their rink when all three teams were there, and just as they should have been taking their place, after their 2011 Worlds bronze, they were dumped the following year, then surpassed by Chock/Bates for a couple of years before earning Worlds bronze in 2017, and weren't that far ahead of Hubbell and Donohue at the 2018 Olympics.
While they won a well-deserved bronze at those Olympics, it didn't look like USFS was that enthusiastic, and Zoueva's politik was dropping after Sochi, and that bronze was not a given, even if a happy ending.
I think they ultimately made the right choice, but they had to have nerves of steel not to second-guess their choice.
I promise I'm not being argumentative nor do I have any interest in turning this into a never-ending discussion. I just want to say one last time that I am actually genuinely confused with this particular situation and don't get how any of the above would have gotten better had they represented Japan...if not got worse by going to a Fed with no strong ice dance history and as you said, with the Reeds not having the most fed support with them.
First, the Shibs won Nationals at almost every level with the exception being the first, Juvenile level back in 2005. They competed at juniors, won the junior title in 2010, and made two World Junior teams and won a silver in 2009 and placed 4th in 2010. Then the Shibs made their senior debut in the 2010-2011 season after Belbin/Agosto retired and medaled at every competition they entered with the exception of the early Challenger event, Nebelhorn (where they placed 2nd in the FD) including 4CC and Worlds, so there was no issue with them not receiving assignments or USFS support, which is a strong fed to have on your side.
Ok, so to be fair, most of that talk of them switching was happening in the 2012-2015 period, but even then they were getting all the international assignments including qualifying for two GPFs, all the 4CC and Worlds, and the Olympics, and I believe as a top 2-3 ice dance during this period they weren't lacking in USFS support.
Even if you think the Shibs lost some ground (after gaining some ground) moving towards Pyeongchang, and had to compete more domestically than they would have if they skated for Japan, they were still actual medal contenders and shared every international podium with V/M and P/C from 2016-17 GPF to the 2018 Olympics. Internationally, no matter what country they skated for, Hubbell/Donohue and Chock/Bates as well as Weaver/Poje, Bobrova/Soloviev, Weaver/Poje, Cappellini Lanotte, Gilles/Poirier, Coomes/Buckland, Ilinyk/Katsalapov and then Ilinyk/Zhignanshin and Sinitsina/Katsalapov, Paul/Islam and Monko/Khaliavin (earlier on and were rivals during their junior days), etc. were always going to be there competing and being contenders/spoilers for medals during this period.
As for Zoueva...the Reeds and Muramoto/Reed still trained with her so it's not like that was going to change had they represented Japan. The Shibs could have left Zoueva anytime they wanted but decided to stay with her.
With all the above, I just don't get why some vocal fans were thinking they should have competed for Japan because they had every opportunity top World competitors were getting throughout their entire senior career.
That on top of other things that showed just how devoted the Shibs were in identifying that they were proud Asian-Americans (being athlete ambassadors for the U.S. State Department in 2012 and then diplomatic envoys after 2016) make it to me all the more strange why there were as many posters as they were saying they should skate for Japan. I know this part tends to be ignored as is the storied history of children of immigrants having experiences of their "Americaness" is questioned, which is actually a big deal to many in the Asian-American community as is my personal experience and one I learned many of us shared when I discuss these things in AAPI circles, I personally found it all strange and more complicated than just seeing this as a situation where a team who may not have gotten assignments or opportunities just to compete internationally having an opportunity to do so by taking advantage of the citizenship of one partner or both. Especially when the Shibs had such a career representing Team USA from as early and as continually as they did.
I know we skating fans can sometimes get conditioned to seeing this as normal (even though the vast majority of skaters don't do this) but I do think this is not something to be taken lightly in
all cases, especially when Japan, unlike other countries that allow dual citizenship, requires renouncement of your initial citizenship and this will affect the skaters for the rest of their lives.