How non-free do we consider Flash to be? The Gnash player appears to be making good progress. Would it be acceptable to permit useful Flash files which work in Gnash and don't require non-free codecs to be uploaded?
I did not see any issues with patents mentioned in the relevant Wikipedia article. The old Macromedia Flash website lists a US patent on "creating gradient fills", but that seems so bizarre as to pose no real threat.
(Let's keep this separate, for now, from the question when a format like Flash would be appropriate, content-wise. I'd like to fully understand the "freeness" first.)