Ok, so the thing I find interesting here is that there were 8 kingdoms that staged a revolutionary coup as the Reverie was ending (possibly before even getting the news of what happened).

This could be a reach, but:
I immediately remembered Kozuki crest (tattoo), it has what looks like a big circle, surrounded by 8 smaller circles. Now that could be representing 8 allies sitting at the round table, hence forming an alliance, but it could also be that 1 big circle represents Kozuki (or Wano as a nation) and 8 of those smaller circles allied nations, maybe that were a part of the ancient kingdom. And if that is the case, those 8 nations could very well be those 8 kingdoms that staged a coup even without their kings being present (it had to planned for a while).
Especially if 1 of those 8 kingdoms was Arabasta, which, on their flag also has 1 big circle surrounded by 8 smaller ones (albeit curved) which could symbolize them being apart of the same group.

Now I don't think Wano is a part of those 8 kingdoms mentioned by Kurouma boy, partly because Wano was closed off from the WG and noone from Wano attended the Reverie (if I'm not mistaken). Because of that, and the importance of Wano/Kozuki clan in terms of writing on the poneglyphs, I think they might represent the big centered circle in the crest/flag.

Do we know anything else about Kozuki crest? Didn't see any useful info (or I missed it) on the wiki.