I've already seen it try to disable sideloaded apps. Was yet one more motivator to go to a de-googled device (specifically DivestOS). I can't do Graphene with my current device, but my next phone will be a Pixel 5.
Currently using an Essential Ph1. Paid $100 for it. Runs fast. Faster than my friends newer phones.
I see no reason to pay hundreds of dollars for a phone. I'd rather pay $130 for a good condition Pixel 5 that has the features I want, and I can afford to keep a testing phone around or use it as a hot spare, and still pay less than a "new" phone.
They could, but I think that would be too obvious. Why such system they could flag it at OS level with a big, scary warning and claim it was for security sake.