the gnome team are developing an app store like installer. It has support for distro packaging backends amongst other things . It will appear in Fedora 20, Suse soon as well with the others to follow.
I've been going over the packages I maintain and have decided to support this effort by helping move this along with some of the stand-out apps.
I've created a patch which creates and installs the metadata file in $DATADIR/appdata according to these specs 
If you are interested, please review. I've grabbed the content/screenshots from the website but you might like to change it. The metadata supports multiple languages, but there's only English in the patch.