There was a bug with Azerite gear and Essences from Battle for Azeroth working inside of these dungeons which Blizzard has confirmed will not be the case come launch.
The Keystones themselves were slightly over tuned, and the difficulty of these dungeons will be decreased by 3 key levels, which puts them at the same difficulty as Shadowlands levels.
Azerite Gear and Essences Will Not Work In Legion Mythic+ In Patch 9.1.5
As Legion was the first expansion to introduce the Mythic+ system, it is by no surprise to see just how far players have come in terms of strategies and overall game performance, so Blizzard may make some changes to try and fix some issues that were not present in this expansion such as, certain snapping positions that are found.
Infernal beacons that do not get activated will now activate once the closest boss is engaged, which will let stronger groups pull off more difficult strategies.
These changes are expected to go live on the PTR this week as we get closer to the end of the update cycle and get closer to a release date each day.
The only piece of major content lacking from the PTR is the Mage Tower, which at this point we can expect not to see it all to keep the challenge for players upon launch.