Very well said. I only use TeX over Word for writing math because emacs 1. makes writing it easy with macros and helper functions, and 2. is able to display the rendered visual snippets inline in the text. If I could not have the second feature, TeX would be borderline unusable, and this dependence on editors and tooling means it's not truly open. Can't envision what could be better for mathematical notation in plain text, though.