'brifter' is f'ing stupid
What? Mavic Shimano/SRAM wheels since forever have been 11 speed compatible. You use the spacer for anything up to and including 10 speed, remove it for 11. Been discussed dozens of times on this forum. And the spacer is metal, not plastic.Shimano/SRAM or Campagnolo?
As for Shimano/SRAM, I'm pretty sure the plastic spacer must stay on with 8-10-speed cassettes: I have two road bikes with Aksiums - one set is Aksium Race wheels which came with the bike, I believe them to be the 2011 model. The other were store-bought and the 2012 model.
The leaflet that came with the 2012 wheels instructed to leave the plastic spacer on for 8-10 speed cassettes. The other bike came built with the same spacer on.
If the plan is to upgrade to an 11-speed Shimano/SRAM drive-train, I think Mavic sells a replacement body specifically for this purpose.
OTOH Campagnolo of course has been selling 11-speed drive-trains for quite a while, as pointed out.