It sounds like the external dimensions are going to be exactly the same or nearly so. I'm hoping the battery compartment is also identical so that third-party mounting and extended battery packs continue to work.
I recently picked up a few of these extended battery packs and it would be nice to eventually upgrade the AirTag if the extended range turns out to be meaningful. They're pretty neat, you remove the battery cover completely and only insert the half of the AirTag with the electronics and radio.