FSSP and ICKSP are going to have to make a decision soon. They will not be allowed to carry on as they have been. Francis has already told us that his plan is to bring everyone back into the novus ordo "in due time" and has forbidden the construction of new TLM only parishes. Then there's all the other restrictions, most recently the taking away of the traditional Triduum in Rome and in Charlestown, S.C. In my book the FSSP and ICKSP should be planning their future right now, a future without the approval of Rome. I think the best-case scenario would be the SSPX returning to their original resistance position and FSSP/ICKSP merging with them. Or they could operate separately with a loose union with the SSPX bishops ordaining their priests.
That would be, in my opinion, a
fantastic idea and a wonderful turn-of events. However, I strongly doubt that the SSPX and FSSP/ICKSP will put aside their animosity/hostility toward each other. I have been to SSPX and FSSP Masses and neither one has ever spoken fondly of the other. I wish this were not true but that has been the case in my personal experiences.
Thus, I believe the SSPX will make a deal with the Modernists to get their "personal prelature" (which I believe, other than
Opus Dei, would be the only other "personal prelature" in the Modernist Church). The SSPX Resistance will gain more members from those who will leave the SSPX but the Indult Groups (FSSP/ICKSP) will lose members because of
Traditionis Custodes and those members who leave the Indult Groups will most likely go SSPX Resistance, Sede (either pro or non Thuc), or Thuc non-Sede (such as the Fraterne de Notre Dame).
Either way, it's bad news for the SSPX and Indult Groups and better news for the SSPX Resistance groups, Sedes, and Thuc non Sedes. Again, I'm not claiming to be predicting the future. It's only a guess from someone who is familiar with both SSPX and Indult Groups.