Ultimately, the makers of Rogue One deviated sharply from the early K-2SO designs. It was, ostensibly, an effort to create something fresh, as opposed to designing an Imperialized facsimile of a droid that’s already immensely popular within the Star Wars canon. K-2SO’s distinctive look definitely serves Tudyk well in letting the droid’s unique personality shine during Rogue One.
It’s curious as to what led the makers of Rogue One to scrap the idea of an alien duo as part of the rebel team. Perhaps they felt that the combination of an oafish character and a smaller, sly sidekick would too closely resemble Rocket and Groot from Guardians of the Galaxy. Maybe they just didn’t want what could be perceived as another Chewbacca. Ultimately, Tudyk carries the non-human torch admirably as K-2SO – and the droid’s more distinct design certainly helped make his performance in Rogue One stand out even more.