> We should have the expectation for private data that the operator cannot read it
That's called heterogenous encryption, and it's the technological equivalent of Mythril. End-to-end encryption doesn't stop the operator from decrypting your data. In fact, pretty much everyone has to, since raw encrypted TLS data can't just get slotted into your OneDrive/iCloud account. These operators literally need to read your data to operate on it. I genuinely don't know how you would engineer a more secure architecture here.
If you want to talk about architectures designed for malicious actors, you probably shouldn't start with distributed systems. Monolithic, profit-driven corporations like Twitter are much easier to tempt with salacious "data brokers, political shadow companies and "the feds""