Originally Posted by
HillRider
That I'm not sure about. I don't know if Shimano changed the geometry of their 11-speed front derailleurs or not. I vaguely recall they have but someone with more definitive info can comment. As a general rule each "speed" increase has resulted in a redesigned front derailleur so it's likely you will need a specific 11-speed one.
Not only that, because the chain keeps getting more narrow the front derailleur cage is also similarly adjusted. You may find that you get slow or no shifting in one direction depending on how you adjust the derailleur. I had this happen trying to use a 7 speed FD with a 9 speed FD (combo wouldn't downshift at all) and a 9 speed FD with a 10 speed chain (slow downshifts).