Auto-promotion here :-D Check Spacemacs, it is an Emacs configuration usable by Vim users out of the box. It has the feature you mentioned powered by the which-key package.
Way better ergonomics than vim and elisp is extremely easy to hack on.
The things I loved:
* helm mode - autocompletions for the commands
* consistency - SPC + ... everywhere
* REPL in a buffer
I understand that a month with Emacs isn't remotely enough to make up for years of VIM, but I didn't find enough benefits to stick with it.