Clever concept, and it really shows off a lot of shell techniques in one place. The self-modifying aspect is fun to study (e.g. external-add, ext_insert), and the meta functions are interesting too (e.g. require). I may find this useful sometime, and in the meantime it makes me smile.
In my own small way, I too have used self-modify shell scripts, though nothing as far-reaching as what you've done. When I write C code, I use a "build" script instead of "make":
https://github.com/chkoreff/Fexl/blob/master/src/build
(Never mind Fexl itself, I'm just sharing the build script here.)
The build script analyzes all the .c files in the current directory and automatically creates another "build" script in the ../obj directory. It then runs ../obj/build. But the next time you run it, it sees that ../obj/build already exists, so it doesn't need to analyze the .c files again.
Again, it's nothing quite like what you've done, but it just illustrates how fun and useful self-modifying shell scripts can be.
