If this is all client side, what’s stopping someone from running MITM and then spamming the endpoint with billions of phony reports?

Hacking charges presumably

I fail to see how any of this proposal can be claimed to have "user consent".

The nice aspect of this is that it will create millions of "illegal" users overnight in the EU. I wonder how it works with Signal when everyone just sideloads the app anyway and keeps using it.

This might collapse the market for computing devices. Dumb phones are a thing.