There's some quite impressive and interesting bash (and other shell) exploration in the matrix.org "Fun Shell Scripting" room from time to time; usually when someone asks an obscure question and a few people dive down a rabbit-hole.

One oft overlooked feature is bash supports dynamically loadable 'builtins' as shared object modules so it wouldn't take much to create a 'proper' wrapper around libncurses.

Debian and derivatives have the package "bash-builtins" that has a lot of examples including wrapping/implementing many coreutils tools.