Some interesting things here...
1. I don’t know if a device that is only capable of receiving radio broadcasts is required to go through FCC testing. I assume this is required for devices that have a transmitter only. Bluetooth of course is bidirectional, while the passive scanning of a PPS transmitter would not be. Looking at Shearwater for example, I only see listings for the Teric, and what I assume is it’s Wireless charging components https://fccid.io/2AO24. The lack of listing doesn’t rule out the possibility of the watch supporting PPS transmitters.
2. I think I found an accidental listing for the watch at this site here: Garmin Descent™ Mk2 Dive Computer Series - Neptonics. It seems to confirm that there will be atleast a sonar transmitter.
It could be an improvement over the PPS transmitter, but given that everyone owns a Shearwater, it would be naive of Garmin to only support a transmitter that isn’t an industry standard yet. Given their support of Ant+, I really hope that this isn’t the case.
Don’t forget that any dive computer that lets you download your log wirelessly has to have a transmitter inside.