it is only a 'marketable feature' if it has no relevance to the story in the film. if it is plot relevant, it is not a marketing feature.
Porgs were a marketing feature, though they were not brainstormed as such originally. the booster on Poe's X-wing was not a marketable feature, though it did allow them to create a new toy rather than reissue the TFA one.
Star Wars has always had merchandise tie ins. it is the nature of the franchise for such to exist.