Unless “read-only” is being enforced by hardware (reading from optical media, etc), a compromised sudo user can circumvent anything, and write anywhere. A read-only flag or the root filesystem being mounted from somehwere else are just trivial extra steps in the way.
Improved security != extremely secure, is all I’m saying. There are a lot of things that go into making a system extremely secure, and while an immutable root filesystem may be one of them, it doesn’t do the job all on its own as advertised in this post.
Courts have ruled that cops can damage property in the course of their duties with no accountability or compensation required, so they’d probably just bulldoze it out of the way and destroy it. And then insurance would say they don’t cover official acts of cops, and then the cops would send a bill for damaging their bulldozer.
There’s probably more fun and effective ways to go bankrupt obstructing ICE.