You are correct in that. I wonder about the ability to create a backup of this existing vimeo forum. If / When Vimeo drops Farsight, then this forum would certainly be irretrievable.
I wonder about tools could be available to port this forum elsewhere. Manually scraping this forum posts for backup purposes would be a start. I suppose we could each back up the threads we follow. It's crude, but browser's "save as html" does give viewable content, albeit frozen-in-time.