Any hardware company which would want to block 3rd party firmware from loading or executing on their systems. They can add a small handshake code to every binary on that system to authenticate via TPM or the processor's embedded secure element on start.

They don't need to make extensive changes. Pull the latest, patch, compile, burn to FW. TaDa!

IOW, TiVoization 2.0. GPL2 makes it very hard already, but GPL3 makes it impossible.

With permissive licenses, it's very possible.

ref: https://en.wikipedia.org/wiki/Tivoization