I can see that...but Nightowl's suit is pretty busy, so it works better for me. Batman's would be black/blue trunks on lighter grey suit - just is a hard sell for me. I'm open to it if done well, but I can't see it happening for the next movie.
Looking at that pic of Nite Owl I realized something for the first time that has probably been pointed out before.
Just like the Arkham Origins Batsuit, if you have Batman wearing some kind of black mesh under-lining and use the grey on the legs and torso it gives the illusion of trunks without actual being trunks on the outside of the pants/legs.

t: