Standards compete on many levels on a give-and-take basis and have very strong incentives to have a minimal amount of complexity. Text editors don't suffer from that set of requirements. This hypothetical editor does everything the others do, cleanly. Almost everyone will agree that it's better. To my eyes the only real problem is that creating the program itself is infeasible.

I disagree. There are already many text editors that do everything each other do, but they all do it differently, some in GUI some in command line, some with different shortcuts, etc. You could argue that Eclipse does almost everything and has a very high level of extensibility and yet you won't get me or many people I know to use it for most tasks. It's not just about some checklist of possible actions it can do. It's about workflow, ease of use, integration with the larger jobs. It's more similar to the "standards" argument than you give it credit for. Other wise everyone would use emacs or eclipse.

Hypothetical is the key here. Everyone can dream up a perfect system, but in the real world, it will have to make compromises, which means that it won't be perfect for everyone.