I've implemented something very similar for upgrading headless Linux mobile robots. One nice property of this approach is that the in-memory installer environment and associated scripts can be common between USB-based install media and a remotely-triggerable kexec type installer.

At first, it surprised me there wasn't more standard tooling out there for this kind of thing, but as I got more into it, I realised how specific to our particular needs my solution had become, and I could see how it would be hard to offer something generic that would be a good fit for a wide range of use-cases without being super-bloated.