ZOS never announces Crown sales ahead of time. While discounts on Crown packs and free ESO+ trial periods have typically happened during Quakecon in August, it's always been part of a larger promotional effort.

IF a Crown sale was happening in relation to Quakecon, we should have known about it already, since the convention is already underway. Looking at the Quakecon schedule, there isn't any mention of ESO, and it doesn't look like any of the keynotes are being streamed by Bethesda either.

Since there is currently a sale on the game, which started on July 30th and runs until August 13th, my guess is there won't be a Crown sale anytime soon. I hope I'm wrong, because I am running low on Crowns and could use a sale.