Command and Conquer Collection would be nice.
So would the orginal Final Fantasy VII on PC without PlayStation DRM, and also possibly opening the door to other Final Fantasy and Square-Enix titles being preserved on GoG (Final Fantasy I-XVI, Chrono Trigger, Dragon Quest, Kingdom Hearts, Star Ocean, SaGa, Mana, World Ends with You, Octopath Traveler, Triangle Strategy ect.)
Currently GOG only has Yakuza/Like a Dragon, Ys and Trails as its major and only JRPG series.