Fast ADS & Unlimited Sprinting
One of the biggest issues with Call of Duty: WWII was that the ADS (Aim Down Sight) time was too slow, which made gunfights problematic and changed the way you had to engage enemies.
With Call of Duty: WWII, going ADS out of sprint felt slow, which the developer said lined up with the play style they were trying to build, but it felt like it hampered the game as a whole. The limited Sprinting time, while realistic, also slowed the game dramatically. We saw some buffs to ADS in Call of Duty: WWII in February, finally.
I'd love to see Call of Duty: Black Ops 4 deliver a better ADS time when exiting a sprint, so that we can move around more in the maps while still staying boots on the ground.
Coupled with that I would love to see unlimited sprinting return, or at least a longer level of sprinting energy to draw on.