I have read over in the AF forum about pax being downgraded from Biz on very busy routes such as PVG-CDG. I imagine award seats would be downgraded before paid business, and hopefully pax upgraded from coach would be downgraded before award ticket holders.
This makes me slightly nervous as I have 4 longhaul AF segments upcoming on a RTW award in J. I imagine you could insist on being reaccomodated on a different flight (with some sort of compensation) in J rather than taking the downgrade.