Can you use SRAM 11-spd trigger shifters such as NX and GX with Shimano 11-spd derailleurs such as SLX and XT? I have read some threads that say these work well together and solve the hard shifting issue with the Shimano shifters.
SRAM and Shimano use different cable pulls and derailleur actuation ratios, so their shifters and derailleurs are nominally incompatible with each other. 

This Art's Cyclery blog page documents derailleur pull ratios, sprocket spacing and cable pull for a variety of derailleurs.

SRAM and Shimano 11 speed mountain use the same sprocket spacing - 3.9mm, so for shifters and derailleurs to be compatible they would have to designed for the same actuation ratio.

Shimano 11 speed mountain derailleurs have an actuation ratio of 1.1. SRAM has two 11 speed mountain uses two actuation ratios: 'Exact Actuation' is 1.3, 'X-Actuation' is 1.12.

NX and GX use the X-Actuation ratio, so maybe the ratios are close enough with Shimano 11 speed mountain that they are compatible. The difference between 1.1 and 1.12 is about 2%, so if you indexed the middle sprocket correctly the high and low sprockets would be out by 3.9mm x 0.02 x 5 =~ 0.4mm.