They still have AppleTV launching tomorrow, so I can see a possible launch some time in November - December.
Just FYI:
The release date for Mac Pro (trashcan) - December 19, 2013
The release date for iMac Pro - December 13, 2017
Both of these were announced previously, though, and only a press release made the world know it was available for purchase. So, for these machines marketed to actual Pros (with little to no expectation of a holiday sales boost because of their price tag), a December release date with no fanfare is quite possible.
I can see them spend all their energy introducing Apple TV+ with an all-out media blitz and then quietly release Pro related hardware (Mac Pro, 16" MacBook Pro) in December.
As for Airtags - I think Apple will want to explain what they are and how you can use them, and I can see them being introduced sometime in Spring 2020 alongside an iPhone SE and new iPad line refresh.