I wonder how it's actually sent. Could you use them on a segregated network and block all DNS requests to the Amazon servers?

This is also too low. Ring pays criticals $12-30K

Doing this without any loss of functionality would likely require replacing Amazon's backend servers.

Which is unlikely but even if done, you would still be sharing data with someone else.

The most reasonable alternative is to replace the hardware. I use Amcrest which supports RTSP. But then you'll need software to monitor and record. I use Blue Iris. But then you'll probably want a way to access your PC remotely to check on things. I use MS RDP but it needs custom setup for reasonable security (custom port, timeout for too many invalid logins, port forwarding on your router, etc.).

All things considered, this ain't happening for most users and I'm pretty sure Amazon knows it.

Would be interesting to find a way to emulate the Amazon back end to either a local server or at least a private cloud account. I think with more and more appliances and other hardware being useless when not attached to a paid service we'll see consumer interest in making it work without the service.

Not sure that consumer interest will ever translate into action unless the "offline" hack ends up being easier to implement than the original service plan, consumers tend to be more driven by convenience over cost. But I think there are a small sub-set of us who just want to actually own what we own.