The news that the BBC has started "encrypting" its RTMP streams came, in one of those coincidences, just as I'd decided to work on adding RTMP support to Gnash. So even when Gnash's RTMP video streaming works, it will still be legally difficult, if not impossible, for licence fee payers who care about software freedom to use the BBC's iPlayer.
Like the CSS technique for DVDs, "encryption" is a misnomer here. Both the technique and the key are well known. The XBMC rtmpdump software already supports it, but leads a shadowy existence after a takedown notice from Adobe. Integrating it into Gnash would be technically trivial. But then it becomes undistributable in many countries.
Just like any other weak and easily breakable encryption technology, it is nothing more than a facade to gain the legal protection of the DMCA and similar laws. Technically you can see it, but because that would involve "breaking" "encryption", you aren't allowed to.
But what can we do about it? How much of an implementation is legally permissible? Can we implement everything but leave users to find out the key on their own? Or write a separate plugin to be hosted in a safe country?