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).