Shimano 8/9/10 speed freehub conversion to 11 speed does not appear possible due to changed spline pattern After remaining unchanged (with a few exceptions like FH-7801) for nearly 20 years the Shimano freehub body spline mount has changed along with the width.  I had hoped I could refit a 8/9/10 speed rear hub (FH-M756) to work with 11 speed.  But the mounting face on the 11 speed freehub body is totally different compared to the old 8/9/10 design.  I don't see any hope in retrofitting old hubs with new freehub bodies.  Anyone found a solution short of hub / wheel replacement?  The "Zinn" filing down method seems to be the only hack available for standard Shimano brand hubs.

FH-M756 freehub body Y3BD98010 cannot be replaced with FH-6800 body Y3CZ12000 (see photo).
There is no remotely practical way of doing it. It's possible that could change in the future as 11 trickles down more, but probably not likely given that the interface is also different on the standard axle, less expensive 11-speed road hubs they've already made.

Just to be clear though, 11-speed MTB cassettes do not require a new longer freehub, because the large cog overhangs.