Marionette is built into Firefox so that might work, except it would require Firefox to implement this as well so it can prove itself.
Your hypothetical change of emulation tactics won't work. You're analyzing at the wrong abstraction level.
The "attestation tokens" to validate the integrity of the web browser environment would come from a 3rd-party (e.g. Google Play services).
For example... Today, hacks like youtube-dl work because implementing client-side code to "solve javascript puzzle challenges" is still inside the "world" that Google-server-to-browser-client present to each other. Same for client-side solvers for Cloudflare captchas. The "3rd-party attestation token" breaks those types of hacks.
Most interesting thing I've read all week.