I get the feeling that most users have only accessed 5% of the features available in their unix shell of choice

I would say not just the shell but most software

And almost certainly languages, too. For example C++.

As someone who has created templated subclasses with both private and public virtual inheritance, I don't think that's a bad thing. C++ is wildly powerful, but it's a mess, and most people should stick to easily understood idioms/patterns, for the sake of maintenance if nothing else.

I also highly recommend enabling the pgdn/pgup bindings for history-search-forward/backward. If you are searching for a prefix it's a bit easier than ^R.

I bound these under C-n and C-p. Very convenient indeed!

I do use this too.