I haven't used a Pebble, but I wanted to mention something I have seen praised a lot on HN and elsewhere. Apparently, the Bluetooth stack on a Pebble is absolutely legendary: reliable, dependable, robust, you name it. It still works reliably today seemingly thanks to their very diligent software design.
I hope that element of it will continue to exist as-is on these new ones? I mention this because Bluetooth is still generally speaking very meh.
Unfortunately, as mentioned in another comment, the Bluetooth stack is apparently one of the items that is not included in the source release[0]:
Some parts of the firmware have been removed for licensing reasons,
including:
[...]
- The Bluetooth stack, except for a stub that will function in an emulator
[...]
Which suggests that the Bluetooth stack wasn't entirely of their own making, so perhaps any of Pebble's own additions were too intertwined (e.g. gave away too much Bluetooth stack vendor proprietary API info) to be easily separated?
I am convinced that there must be Pebble fans on the Android team that keep a Pebble in CI and ensure it keeps working with each new release. Otherwise its continued extended working lifespan is inexplicable given the amount of churn in Android in general and the Bluetooth stack in particular.
Not as crazy of a theory as you might imagine. Years after death and acquisition after acquisition, a mystery Googler recompiled the long-discontinued Pebble app with the original signing keys so that it would work with new 64-bit app requirements.
Actually kinda to the contrary BT is extremely back-supporting. It adds/removes features so slow that it’s too boring. That’s why I left my BT expertise at the start of my career and moved to app development (it was a mistake in the hindsight but that’s another story).
Sure, it's backwards compatible in theory. In practice I haven't had any device that kept working reliably with zero issues through every Android update and every phone upgrade. Including very important ones like Tesla's phone key. Even Pebble wasn't flawless at the very beginning, but it got good fast and hasn't stopped working since the company went under.
I hope that element of it will continue to exist as-is on these new ones? I mention this because Bluetooth is still generally speaking very meh.