Disney is massively protective of its characters, especially what it calls the "core characters". Even Disney-authorized travel agents are told that they can never, I mean never, display an image of Mickey or Minnie Mouse without prior written authorization. There are a handful of artists whom Disney has granted a license to use their characters in specially-cultivated artwork and if these artists try to post their own art that uses licensed characters on their own Facebook accounts, Disney brings out the lawyers. They are rabidly, ridiculously protective of these characters and brands because they don't want to ever risk the consumer getting sick of them or associating them with something negative.
Although Disney would continue to own the Mickey Mouse trademarks, you can probably tell that they wouldn't be fond of the potential dilutive effects that may flow from the free commerce of public domain works involving these characters. To them, Steamboat Willie going PD is the death knell not only of the Mickey Mouse cash cow, but the entire brand icon empire (without which Disney becomes little more than a mediocre theme park destination).
Although Disney would continue to own the Mickey Mouse trademarks, you can probably tell that they wouldn't be fond of the potential dilutive effects that may flow from the free commerce of public domain works involving these characters. To them, Steamboat Willie going PD is the death knell not only of the Mickey Mouse cash cow, but the entire brand icon empire (without which Disney becomes little more than a mediocre theme park destination).