Incidentally, the sequence of demotions is based on the relative values given in Who is Who on Eight by Eight (http://www.chessvariants.org/piececlopedia.dir/whos-who-on-8x8.html). The only difference is that WiWo8x8 ranks the knightrider below a bishop (probably because it can move to and threaten fewer squares on any given turn, despite the fact that it's not colorbound like a bishop is). I just didn't want to have a simple piece demote to a compound, as that'd be pretty weird.

There may be a better way of ranking the pieces for demotion, though.