I would expect the Parsons, M/C, and C/P to get 2 spots. They did this year and they each earned a medal.
I do believe they can each get two spots. That said, this is exactly why I wouldn't take it for granted that they will be easy to place for a second invite at a non-host event. They have one spot guaranteed. They don't have a second one guaranteed. And they all medaled. This means, they are a problem everywhere. They are a problem for Lauriault & Le Gac and Galayavieva & Thauron in France, for Lajoie & Lagha/Soucisse & Firus/Fournier-Beaudry & Sorensen in Canada, for anyone who gets the third & possibly the second berth in Russia. And for the current national champions in China and Japan. (Probably Japan won't care. Most teams on the GP will be a problem for Komatsubara & Koleto).
Anyway, I think six teams ought to be placeable; but it may take a little work and some strategy to get them. And a host spot or two.
Or they could protect H/D and hope that Chock/Bates do well against opponents in an away-field. As usual, whoever gets China or Japan gets a break because the local teams aren't that strong and it's neutral territory for the battle at the top.
This is true for talented young teams just trying to break in, at least in China where all the host spots are often filled. But neutral territory often means the toughest battles at the
top, since the top teams would rather meet their major competition in neutral territory than in someone's backyard. (Plus NHK is popular as there is money to be made touring there if you can develop a fan base). It's not an accident that Virtue & Moir, Papadakis & Cizeron, and Cappellini & Lanotte were all at NHK a few years ago. China had Papadakis & Cizeron, Chock & Bates, and Bobrova & Soloviev the last time it was held.
Having said that, I do think Chock & Bates could quite possibly have a better route away this coming season. Stepanova & Bukin and Weaver & Poje won't be in any of their fields. Plus it wouldn't be a bad thing to get a crack at a win over Sinitsina & Katsalapov, who will most likely be in China. There is the possibility that C&B could wind up at Rostelecom; but if that's going to happen, it will likely happen whether or not they go to SA. SA is pretty likely to be one of the tougher fields if C&B attend. If they do, the odds are all-but guaranteed that either Gilles & Poirier or Guignard & Fabbri will be there. (And Zagorski & Guerreiro wouldn't be a huge surprise as neither of the top two Russian teams would be there). That said, the reality is that you have to be able to defeat those teams no matter where you go. It could look different in the fall--or in June if we get surprises for who signs up for the GP; but as of now, the top six look likely to be well divided up.
Which just reminds me of how pissed I was that USFSA didn't name them as the #3 alternative to Worlds in 2016 and instead left that slot blank. That would have bumped them up an envelope.
