You know what would be really cool? If the ‘gorilla walkers’ were actually manufactured during the height of the Empire for a specialized combat situation and have been heavily used by the First Order since. I could see them in formation with the more ubiquitous AT-ATs and AT-STs, and this would answer the question of where the First Order gets all this new tech. It could be the case that since the Empire and the Rebellion fought on many battlefields beyond those seen in the films, the Empire could well have a vast array of unique ships and vehicles as-yet unseen, just as Rogue One has shown.