Just what the title says. Give the colossus tank rounds some knockback capability. Imagine the physics of an orbital strike but on a much SMALLER scale. Shell lands near a group of infantry? laugh as they sail up 15 feet in the air and (possibly) die from fall damage. Weak damage against enemy vehicles? No need to increase it, watch your round hit enemy vehicles like a charging rhino, causing them to miss their shot if you time it just right or cause them to flip if they are already in an unstable position. I think this is a way for the tank to feel powerful without actually giving it a straight damage buff.
I think that would be much more interesting than it just doing more damage. Personally however I would hope for a new addition of an artillery cannon. You would have to swap out the Skylance for it. Kinda would turn it into a big version of the Starcraft 2 Siege Tank.
It used to knockbackeffect every groundbased vehicle right after release. Last week I wondered why they got rid of it.