Automatic publishing from version control
I'd love to see a standard, central, and single Emacs package manager. Right now, I'd put my money on ELPA, but there is still a long way to go.
The biggest thing that would help an Emacs package manager would be to make it super trivial to publish packages. In my opinion, I'd like to see this happen in combination with a version control system like git on a central hosted platform like GitHub -- something that would make it easy for authors to publish their packages and would make it easy for others to contribute back.
Similar to how GitHub (used to) make it easy to publish RubyGems, I'd like to see something similar in an Emacs package manager. For example, tag your repository with "vX.Y.Z" and have your elisp goodness automatically available to all.
The added benefit of using a popular backend like GitHub is that you'd immediately get a lot of exposure which should help drive its success.