It should not really impact any of the devices or accessories. The changes are only to HomeKit itself.
My understanding:
This architecture change is only to how Apple queries and tracks devices.
Before the HomeKit architecture “upgrade” - every time you open the Home app, the app would query each and every device on your HomeKit network for a status. Every interaction with anything in the Home app would cause a re-querying.
What the upgrade essentially does is changes that model.
Now one of your hubs will keep track of the status of the devices. Your Home app will only ever need to communicate with a hub.
Reduces network chatter a ton, reduces need for devices to wake up and respond all the time, probably saves energy in the process, and makes everything respond much quicker.
I am sure there are other changes or tweaks as well, but it is this major fundamental one which makes it not backwards compatible.
But the upgrade process is clearly buggy.
Now that it is working correctly for us though, things are - what is the word we use here in the Apple fanboy world? Oh yeah. Things are “snappier”.