The forum "mirror" is up: https://tmptesting.godotforums.randommomentania.com/
(It is not a true mirror and instead is a snapshot of the forums from 20-40 minutes ago - it also will not update as new posts are made)
It is a completely standalone instance. Right now it just uses the default Flarum theme but I am working on a new theme. I do not have anything to share yet though as I only just started. I am building it off the OXO theme, which is what we are using now.
The forum "mirror" is a read-only forum though - it is not intended for posting and is really just to get feedback on the forum theme. In the future, I may make it possible to post for testing plugins, but for now it is read only for everyone but forum staff.
I'll make an update here when I have the first draft of the new forum theme ready for the first view 🙂