The new items system made the theory of AP Vi becomes true, theoretically, Vi can go AP due to her E in the last patches, but tbh there wasn't a certain win-guaranteed, or at least, winnable AP build, and it has to be classified as worst choice ever.

After the reappearance of Stattik, Vi can get benefit from the item's ap scaling, which would be helpful in farming and ARAM fights, also it gives Vi a decent amount of attack speed and crit, which would be helpful in fights and clearing farm.

Not to mention that Dark Harvest is a very toxic rune despite adaptive scaling you're, but it behaves very well with ap champs, if you collected a decent amount of souls with enough ap points, your E will work like an atomic bomb, especially with champs who don't build health or armor "like most of adc/supp/mid champs."