They're a big part of what make Emacs useable for me.
I have set up hydras for pretty much every major mode I use (except magit, which kind of has its own hydra-like menu system).
Because of hydras, I don't have to remember all the arcane keyboard shortcuts these modes have bound by default, and don't have to look up how to run a function that's not bound at all.
All I have to remember is one keyboard shortcut which I have configured to bring up a hydra in every mode, and it'll show me a menu of everything I can do in that mode.
This is really fantastic, has revolutionized the way I use Emacs, and has made it 10 times as useable for me as it was before I used hydra.
I wish 'UI autocomplete' like this was a standard feature of operating systems. GUI's aside, how nice would it be to run a CLI command with some flag that allows you to explore the various options and string them together, rather than reading the manpage and searching for whatever flag you might want to use?
A slightly nicer embedded docs. They were great for 80s way of life, but it could use a slightly more reply (to stay in the context of a live editor / lisp machine). Maybe a text demo system.. after all you could script a demo of workflows in elisp for newcomers to see rapidly.
- hydras could be extremely useful for newcomers for instance (and I'm no fan, but it cuts the chase by a factor of 1000)
- ace-jump
I don't know, I'm just suggesting