Yes, it's quite brittle. Looking over your list, part of the problem is also that it was written to function as a WYSIWIG system in an environment meant for tex

Yes, it's quite brittle. Looking over your list, part of the problem is also that it was written to function as a WYSIWIG system in an environment meant for text buffers (rather than a generic MVC like framework where you could apply an arbitrary transformation on the on-disk data to present on the screen). If you're a power user who would like a very malleable system, I can't imagine anything better than Scribble/Pollen. IME it felt very natural to use, and is infinitely flexible (fully-programmable in Racket).