They would just start obfuscating the data (with ciphers, word replacements, encoding, minification, etc.)
They'd then claim it was for your security/privacy/protection. You know, like how Microsoft encrypts your Windows 10 usage data it sends them.
At least you could use the presence of such obfuscation as a sign there's probably something bad afoot. Presuming only a tiny number of extensions try to encode the data they send.
I do not think collecting data on users is necessary. You still can show ads in search results even if you don't know anything about a user. And you don't need user's browsing history to sell him an airplane ticket.
Most people would just press "Agree" without reading it, but giving the possibility to read the data only when you want would give to expert users the way to occasionally check what the addons are doing.
They'd then claim it was for your security/privacy/protection. You know, like how Microsoft encrypts your Windows 10 usage data it sends them.
At least you could use the presence of such obfuscation as a sign there's probably something bad afoot. Presuming only a tiny number of extensions try to encode the data they send.