[qrmn]

Absolutely. I built a concept that essentially did that.

Separated program and data memory with only one executable. USB host would get (in hardware) an outright memory dump of the program memory on connection, so it could hash it/compare it to known-good firmware. If you flashed the firmware the data memory should get wiped, and if you flashed it with anything the driver didn't know as a good build, unless you manually whitelisted it, you'd be warned.

That seems like a better approach to me. (It turns out I really suck at designing hardware, let alone secure hardware.)

Doing the same kind of general thing with, say, a RISC-V microcontroller and trying to secure the RAM seems like a generally fruitful possible course of action? Let's see how Lowrisc turns out.