this would be a great mechanic not only gameplay-wise, but also closer to the way mortars work in real life.
i'm not too experienced with the modding tools, so i'm not sure how difficult it would be to implement the zeroing effect exactly as you describe. however, decreasing scatter with each consecutive shot should be possible, since a lot of offmap a ilities work like this already. another good example (although kind of inverse) would be the brummbär's bunker buster barrage, where the last 2 shots have higher scatter than the first one. afaik this works by calling different weapon profiles depending on the number of shots fired, something that could easily be applied to mortar barrages, too. not sure if this would be possible for auto attack though.
Agreed.
Any movement of the mortar whether it be moving to a new location or rotating should reset the scatter. Is that something that can be done?