Others have pointed out the problems of trolls generating racist or otherwise controversial content using Disney characters and this being short-sighted by Disney, but I think this could just be another case of "no such thing as bad PR".
People will undoubtedly generate reprehensible things using these characters, and I think that's exactly what Disney wants because it's an easy way to make their characters go viral.
It's strange though because if you know anything about Disney and how the manage the characters in media and at the parks, they are extremely protective of the brand and image of the characters. Imagineers have very strict rules around virtual character meet and greets and etc.
Allowing their characters to be used in AI generated content blows that all out of the water unless there are some extremely tight guard rails.
They are a half step from flooding the market with Disney Princess porn.