A little V'idea
I was looking at Vi's kit and I was thinking she could use a little top-down love. So step 1, buff the defensiveness of towers just a little. Maybe buff their HP Step 2, let Vi's W apply to towers as well. If Vi can break a vault, she should be able to break a tower.
Doing this would solve one of the problems in the game right now (towers made out of balsa wood) and give Vi a lore-friendly mechanic.