there is 1 other factor in getting the shows on GOG: Funimation, sentai, and Viz have shows on itunes. Their contract with itunes may mean they cannot bring them to any DRM free places (if that is the case, fugga 'bout Ranma coming). All 3 also have shows on hulu/free streaming media which again, contracts may preclude them coming to GOG. Also, contracts between Anime Network (Sentai's on-demand channel) and <insert major cable provider here> are a probable hurdle as well.
Not mentioned in the above list of shows is for shows like Sword Art Online, Kill La Kill, and Fullmetal Alchemist (anything involving Aniplex in the production or if it says it on the front of the set), you need to deal with the following companies (all of whom answer to the Japanese branch-I may be making a couple up but you get the jist): Aniplex (Japan), Aniplex of America, Aniplex of Europe, Aniplex of Russia, Aniplex of South America, and whoever is the Australia lisencor for their shows. If the head office in Japan says no then say sayonara to seeing these shows until management there retires and policies change. Also, even IF they agree, expect them to price very high ($40 for maybe 13 epsiodes)! because you can get dual-audio and DRM free so they need assurances they people won't pirate (they are also on itunes US but FMA is not. Pricing there is in-line with other shows but that is probably Apple's policy not Aniplex's doing).

I'd rather see something like gog dabbling into releasing drm free android games (actual ones for phones/tablets) or something.