I’m still learning Emacs, so I haven’t had a chance to look into package managers, but a great feature would be to inform the user that the package is available if they try to use it but it’s not on their system. For example, I wanted to edit a PHP file on a server once, and I tried
M-x php-mode
and Emacs was all like
M-x php-mode [no match]
when it should have been like
php-mode available from ftp.gnu.org. install? (y/n)
and then it would have installed and loaded up php-mode for me. That would have made my day right there.