Hi wtolkein and welcome to the forum!
Here is my understanding of the situation and hopefully it will help you in your investigation. I’ve done some basic Bluetooth hacking and have a variety of sniffers, transmitters, receivers, etc. to mess around with that stuff and am very eager to see the new LE audio standards and support to begin rolling out to hearing aids and other devices. Hopefully this information will be helpful.
I don’t believe HAP/HAS is needed for 3rd party devices to work with hearing aids and the new LE Audio capabilities including the Auracast. HAP/HAS is optional and I think is focused more on interoperability between 3rd party devices and hearing aids across any manufacturer allowing remote control of programs, presets, volume, microphone gain, alerts, etc. Today, every manufacturer sells proprietary remotes or has proprietary software on the mobile devices to remotely control the hearing aids. In the future, the 3rd party device needs to be able to interact with the hearing aids to introduce new functionality, especially related to using the microphones in the hearing aids to transmit the users voice to interact with 3rd party devices. That level of integration controlling the gain levels of the hearing aid microphone without necessarily increasing the volume level of the receiver in the user’s ear. HAP/HAS provides remote control capability at that level.
I’m not very clear on the purpose of the unicast capabilities, but it seems like that is focused on extremely low latency communication such as broadcasting audio at a live event and having it synchronized with the person speaking into a microphone. That’s not much of an issue to deal with in a movie theater or TV since those already have latency correction capabilities, (lipsync) to keep things from looking off. Unicast looks more like extreme latency priority over audio quality.
If the Moerlabs device has base-level LE Audio, it should work just fine with a hearing aid claiming to support the same base-level of functionality without any need for HAP/HAS.
Capabilities like broadcast audio for Auracast have more dependencies above just the LE Audio streamer since you need to have the Auracast Assistant in the mix to direct the hearing aids to tune to the correct channel. It was looking like it would be a long road until everything would be in available and users had upgraded all of their devices, (mobile devices and hearing aids) with devices that support the LE Audio standards. There was some good news a few weeks ago when the Bluetooth SIG made a blog post with a new developed guide titled: Accelerating Market Adoption for Auracast™ Broadcast Audio. This guide describes how manufacturers and developers can work around an end user that may have new headphones or hearing aids that support Auracast, but they haven’t upgraded their mobile device. It’s pretty clever and should open the door to get things moving a little faster.
Blog Post:
Guide from the Bluetooth SIG:
https://www.bluetooth.com/wp-content/uploads/2024/02/2401_Accelerating_Auracast_Adoption_FINAL.pdf
Kind of a late-night brain dump on what I know about this stuff, but looking forward to hearing about what you discover and comparing notes.