On my Specialized Rockhopper hardtail I run a Shimano 3x10 drivetrain. The derailleurs are both XT with the front mech being model number FD-M781. For an excellent price, I can get a new take off XT front shifter. However, the model is SL-M8000-L (Left, front, 2/3 speed) and is marketed for 11 speed systems. So, with my 10 speed front crankset being Deore FC-M610 42-32-24, can I expect the M8000 front shifter to move the M781 front derailleur smoothly between the chainrings? I've had excellent luck mixing Shimano 9 & 10 speed mountain front drive components and hope this will be the case here.
All signs point to yes. The differences between 10 speed chain width and 11 speed chain width are minimal (5.88mm vs 5.62mm) and although the spacing on the cassette is narrower for 11 speed the front chainring spacing is often the same.