So, <http://people.opera.com/philipj/2012/04/06/big5-foolip.txt> is the mapping I suggest, with 18594 defined mappings and 1188 U+FFFD.
Awesome Philip!
The specification has been updated accordingly. I guess I should write some blog entry to summarize the whole exercise in case implementors need convincing.
http://dvcs.w3.org/hg/encoding/raw-file/tip/Overview.html#big5 -- Anne van Kesteren http://annevankesteren.nl/
