SRAM X01 Eagle (12speed) in 11speed transmission: it work? Well, I intend to use an SRAM X01 Eagle (12speed) rear derailleur in a 1x11 transmission (with a SRAM X01 "non-Eagle" 11speed trigger, cassette SunRace 11s 11-46, SRAM PC XX1 chain).
Will it work perfectly?
To quote Art's Cyclery:

"Eagle drivetrains are not backwards compatible in any way (the exception being SRAM’s direct mount cranksets, which will still require a new Eagle chainring)"

and VitalMTB:

"SRAM will only make the Eagle chainring in the direct-mount style at first, and we were told it's the only Eagle component compatible with their 1x11 drivetrains. No 11-speed products will work on Eagle."