Details! is still working on it, for example. Github would allow anyone to write their own addon management software AS WELL as fork AS WELL AS push updates to help authors.
If you're writing Addons in WoW for money you're going to have a bad time.
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Hashtags are probably the only (practical) method. This particular topic is something I spent a fair amount thinking on and that particular problem is difficult.
Personally I'd be ok with Blizzard hosting the model for addons via git repo's. It'd make discoverability easier as well as many other things but WoW's dev's don't seem interested in resolving those particular problems. Who knows, maybe doing that would cost us a tier or something.