Lutefish: I suspect you can answer your own question. I don't think the sky is falling, nor are any major empires dead yet.
But the list of skills that you would test or compete at each USFS level would change. Eventually that might be true for ISI levels too.
I'm not sure, but the nominal standards for those skills might also change, especially for the USFS. So if you want to be rated well, you might need to change the exact style you use.
Your coach's hair may go grey trying to figure out exactly what has changed. He/she may end up taking classes to help him/her figure it all out. He/she may try to pass on the costs to you!
Judges will also have to learn the new standards. So there might be slightly fewer available? Or your club might push you and others to become judges.
BTW, since the USFS has already started mailing out materials for the new LTS program, I assume that those standards still apply, for the current season, unless there are mid-season corrections. Likewise, the current ISI Handbook
became effective 9/1/2016. Even if their eventual merger is slowed or stopped, I don't see how they could reasonably immediately cancel those changes made for the current season.
Now wouldn't it be fun if everyone instead adopted the standards of the ISU?