I think the key problem here is where and how do we establish a root of trust for Web applications. Currently we have some form of root of trust for HTTPS/TLS,

I think the key problem here is where and how do we establish a root of trust for Web applications. Currently we have some form of root of trust for HTTPS/TLS, code signing, trusted execution, that the OS or browser or chipsets distribute a set of "trusted" root certificates. For the consumers, they are implicitly backed by the big companies that manage the screening, auditing, and distribution of these certificates. But of course, these certificates have limited use cases that not yet covering the end-to-end encryption application for Web. One way or another, we have to start our root of trust at some layer, either it's hardware, OS, drivers, or applications. But in general, the lower the layer gets, the lower the risk would be. Because it's easier for an evil actor to target specific user in higher layers. There are more to be solved than just the root of trust for E2E on Web. For example, even if we can use trusted execution environment on a Web application to ensure secure key generation and key escore, we still have to face the problem of how to input or present the cleartext data with the user. If we still let the JS code to handle the cleartext in any way, there could still be a chance that the distributor of the JS code might steal them. With that said, not only should we have a root of trust, but we also have to trust the UI provider that operates on the sensitive data for user input or display. The lowest UI layer is usually the OS, so even we have hardware root of trust, but if the trusted UI is in the OS layer, we would still be throttled at the level of trust on the OS layer.