I'd argue the big determiner of whether or not we get another FFXV collab depends on the nature of the FFXVI collab. If it's in the same vein as XV's, with a short world quest, then I'd argue it's less likely. If, however, it's closer to the Monster Hunter collab (permanent new content), then an FFXV crossover rerun would be more likely, possibly soon-ish after Dawntrail's release.

If memory serves me correctly, Yoshi-P mentioned that the Yo-Kai event is up for a possible rerun soon-ish. The FFXI event is absolutely getting a rerun sometime during Dawntrail, and Dragon Quest might be sometime during Dawntrail, however, I'd argue it's probably the least pressing of the events to rerun.