As was already pointed out, it may not be possible do to restrictions already in place. However, if it's not a restriction, what about those who are using clients that can not be updated? How would they be able to view the extended colors?
I have a recommendation though, which I think everyone would love. For the viewers side only, dual color sets, and when colors are being used, the foreground set and the background set would be slightly different. Just enough so that, say, (ctrl-k)01,01 wouldn't produce black/on/black, but perhaps a very dark shade of grey on black, that way you don't have to highlight the line to read it. Would make peopels lives so much easier.
