FYI, they are working on a new “Resonate protocol” for Music Assistant and ESPHome that will be part of the underlying enabling software technology solution needed make this happen someday:
A workaround today is that you can just connect high-quality external amplifier + speakers to the audio output jack on the Home Assistant Voice Preview Edition (though such a solution only works for single-room setups so you can not currently use it in as a proper multi-room audio setup as-is):
PS: As for Google Home / Google Nest smart speaker replacements check out the DIY drop-in PCB repacement hardware for Google Nest Mini / Google Home Mini speakers that iMike78 is working on: