It's also worth noting that Shimano just announced the new CUES platform which unifies the 9, 10, and 11 speed drivetrains to make all of the various parts in t

It's also worth noting that Shimano just announced the new CUES platform which unifies the 9, 10, and 11 speed drivetrains to make all of the various parts in that range cross-compatible. You already could mix-and-match in a lot of cases with a bit of creativity, but now it'll be an officially supported configuration and they're greatly cutting down on the number of unique parts.