As much as I prefer real native applications and like hating on electron, I have to give it some credit. It is not just chromium, it is chromium+nodejs and all the stuff that comes with it.

The answer to "would it be feasible/easy to port an Electron app to a pure browser app" is no. Unless all of the communication between the frontend part and the native tooling is done via sockets.

I agree that native apps should be sandboxed, however sandboxing something like an IDE will be quite difficult. Even Apple does not sandbox Xcode.