That's arguably the problem of the common interaction patterns in GUIs being non-modal. Could've been easily solved early on by having a convention like "holdin

That's arguably the problem of the common interaction patterns in GUIs being non-modal. Could've been easily solved early on by having a convention like "holding Meta (Alt) makes all text on screen selectable" and sticking with it. At this point, it's not even a technical problem anymore - it's a social one. Even if somehow OS and browser vendors all agreed on a scheme like this, copyright industry and security people would scream bloody murder and prevent it from being implemented.