Even if they don't brick them explicitly they will no longer provide security updates for them.

I'm on the same boat, smart TV has never been online, all content is just cast from media server/phone/tablet straight to chromecast. It works, no fuss, glitch free, and of course they will kill it.

Even if they were to provide security updates, a few platforms no longer work with them. At the very least, now Disney+ refuses to stream to my original chromecast dongle.