We still have the key for the onion we previously had. The bug why we turned off the onion previously should be fixed by now.
The Debian mirror serving over an onion (T399) seems to work. So we should get the onion for whonix.org back online.
Subdomains (phabricator.whonix.org and forums.whonix.org) are problematic. So we might just do it for www.whonix.org.
But maybe there is also a solution for sub domains? -> https://gist.github.com/mtigas/565718bbb928ce439e95
Does letsencrypt help with onions? -> T443