While I eagerly await a built in wake word function, I decided to see what other options are out there and started looking into open source hotword detection projects, and found snowboy. Combining a snowboy plugin with tasker and an android tablet connected all the dots to run local wake word detection that drops seamlessly into the assist service.
The only downside is that recognition for custom phrases is fairly limited (custom wake words are based on only 3 audio samples from the intended speaker), though it seems possible to use them, maybe even to setup different access per speaker, but I haven't gone down that path yet.
Thankfully there is a small selection of "universal" built in wake words including:
Hey/Ok Google
Alexa
Jarvis
Computer
Snowboy
Smart Mirror
and a few other oddball ones that can be found here: https://github.com/Kitt-AI/snowboy/tree/master/resources/models
In short, using any android device (an old phone or tablet), install "Tasker" and "HotwordPlugin" which uses snowboy for the local wake word detection. Assuming you have the assist pipeline setup already and the home assistant app installed, have Tasker call the HA apps assist service whenever HotworkPlugin detects the wake word and triggers the routine. Set it to launch a new assist service with every trigger so it will take consecutive commands.
Depending on how the wake word functionality is implemented in HA eventually this may be just a temporary solution, but it's working well enough for the moment.
Tasker: https://play.google.com/store/apps/details?id=net.dinglisch.android.taskerm
(It's a paid app, but well worth it considering what you get for $3.50)
HotwordPlugin: https://play.google.com/store/apps/details?id=nl.jolanrensen.hotwordPlugin
(there is an ad supported free version as well)
Snowboy: https://github.com/seasalt-ai/snowboy