They're probably not just going to shadow-drop a new trailer- traditionally, they tend to give us a few days' notice.
For USUM releases:
August 18th - No heads up
September 13th - No heads up other than a DIrect existing
September 22nd - No heads up
October 5th - No heads up
October 12th - No heads up
November 2nd - Heads up
November 14th - No heads up
With Let's Go, there were several reveals
July 12th Video - No heads up
August 3rd Video - No heads up
August 18th Video - Heads up in Pokénchi summary. No international heads up
September 10th Video - No heads up
September 19th Video - No heads up
September 25th Video (Meltan reveal) - No heads up
October 10th Video - No heads up
October 18th Video - No heads up
October 25th Video (Melmetal reveal) - No heads up
November 7th Video - No heads up
I think the times of us getting a heads up are long passed