Basic things that need to be done.

Termcap or terminfo support for keybindings.
Fix window resizing.
Better documentation.
Handle commands that are too long to be passed directly to the shell.
'vi' specific features that need to be added.
Finish implementing range and count for user commands.
Key mapping for :nmap s
Named registers for yanked or deleted files. Possible things to add.
Use system wide mimetypes file. /etc/mailcap?
Virtual File System If you are interested in playing with the source code.
texplorer.c contains main() - which does basic initialization.
ui.c - setup_ncurses_interface()
signals.c - setup_signals()
keys.c - main_key_press_cb() - the main loop.