> TeX is a poor foundation to build upon

I still disagree with this characterisation. TeX is a really beautiful solution to a non-trivial problem, and its implementation in WEB is really quite interesting. LaTeX adds quite a lot of complexity and messiness, but does also add very useful functionality and abstraction away from low-level typesetting. Org-mode and similar 'mark-up' languages are very nice in more rigidly-defined domains, but they don't have the power of (La)TeX for academic writing. I don't see any real 'competitors' to (La)TeX that aren't themselves just adding layers on top of TeX (for better or worse). TeX is nearly as old as (original) Emacs and has similarly become complex in perhaps not-entirely-ideal ways, but - like Emacs - there's no substitute.