You could dig deeper into software archeology and go with TECO, the editor that EMACS was first written in. It would be silly to do so, however.
- More customizable than emacs
- more mature community and 'giants to stand on' (like packages)
- Stronger expected lifespan
- Realistic enough to actually commit to (not like, build the universe, build your OS from scratch)
I'd love to hear if there's anything you've found beyond the Mariana Trench! Will