I think I found a use case, but would love to be proven wrong with some faster / cheaper approach:

I've tired of buying S1 compatible sonos speakers on ebay, so I'd like to build a speaker enclosure with a WiFi device that has a high-quality DAC and the ability to use pipewire or similar to do real-time DSP and multi-room audio sync.

A RPI + third party hat should work well for this, or so I am told.

This sounds like a great approach to me. I've thought some kind of pi zero 2w based smart speaker system would be an awesome project for a while. I am having a difficult time imagining a cheaper option, especially if you want something like the hat ecosystem.