Blocking audio on specific subdomains could be useful for some people, so I'd rather not remove that feature. It might be a good idea though to add some way to block audio for the whole domain (*.example.com) or specific pages (example.com/example). I will have a look at that.
Blocking autoplay videos is actually pretty difficult, because as far as I know, you basically have to implement it separately for every player/website, which is a lot of work, prone to breaking on changes, and difficult to maintain. That's not really something I plan on doing. A workaround might be disabling media.autoplay.enabled in about:config, which disables autoplay on all sites.