That's irrelevant.

A self-updating hardware/software combination from Google can never be a long term solution. Reliance on old units from eBay (or not!) cannot make that situation any better nor any worse.

It is Probably just fine for the next 10 years. Chromecast audio are working great for me with my 70’s receiver and modern mini amp and Bluetooth speakers with line in.

There are companies out there that make similar devices now luckily (sadly they're more expensive :/ )