The excitement about Mickey Mouse maybe kinda sorta being available for public use is mostly about the novelty of it, mixed with some schadenfreude towards Disney, which, fair. But I don't see it really being that big a deal in the long run, and certainly not for our genre. Lots of characters are already public domain and it's not like any of them really revolutionized TTRPGs. The Lord of the Rings is still under copyright but that hasn't stopped it from being massively influential because ultimately it's the ideas that matter more than specific characters.
What's important about Mickey are the ideas that helped make him popular, and those have long since been strip mined and incorporated. Building a D&D adventure around "Steamboat Willie" is a cute novelty idea that has zero meaning for the game.