The option to disable long grass has always been there afaik, this sounds more like a tweak to allow more options between Off and Very High. ArmA doesn't render grass at distance anyway I believe so this shouldn't affect too much far away but close up may be another story.
ArmA has always had issues in this regard with all environmental cover like grass, bushes and trees, I think even rocks, rock walls and debris may be in this category. Even though the tree is there, the full image does not block AI view which is why you can get killed by AI without ever knowing they are there. The AI view block is extremely low poly and is never the full size or shape of the object it's attached to.
There was a project that worked pretty well to fix this issue but I think it was scrapped because I haven't seen anything of it in a while; maybe I'm just not looking close enough.
I don't think there will be a way to turn off trees and bushes though as they render as very low poly blobs when set to their lowest settings. This also sounds more like a tweak (a much needed tweak) to have trees and bushes scale properly at more distances.
...if you've ever just stood in place and zoomed into and away from a tree, you'll see exactly what I'm talking about.
