Your comments

I mostly agree, but bundling a package manager with a whole new GUI is not the best solution.

What we need is a website where all packages can be browsed, maintained by owners themselves, and maybe a simple command-line utility to install from a git repo or .zip/tar file.

Then if you want to get fancy you can use a registered extension (.sublime-package) or protocol (sublime-install://) that allows one-click installs. Following something along the lines of textmate where myplugin.sublime-package would be just a zipped folder and auto-installable would be nice.