Dura-Ace 11-speed Cassette...

[aatores]

...can they fit on a Dura-Ace 10-speed freehub?

[cfox]

nope. 11 speed free hub is close to 2mm wider I think

[dvs cycles]

Must use Shimano 11 hub but Mavic Kysium works fine for me.

[oldpotatoe]

...can they fit on a Dura-Ace 10-speed freehub?

No, shimano 11s compatible FH only..shimano 9000, some of their latest wheels, mavic, Fulcrum..Campagnolo does make a shimano 11s FH for Campagnolo hubs/wheels/Fulcrum wheels, BTW-I gots 'em.

[sailorboy]

DT swiss hubs are also_sort of_compatible in that you can get the 11 speed rotor for about $100 and pop it on there without much in the way of tools and run 11 speed without re-dishing/building the wheel. Same with campy splines on 240s hubs.