Part of the reason I mentioned song or story (vs. visual format e.g. a comic) is because it allows the consumer to fill in the visualization themselves. Thus, while using the 'Steamboat Willy' version as a creator, the audience is free to substitute their conception as they please. No doubt I'm working a fine line here, but a catchy song about "Mikey Mouse on the River" could pretty much hit the factors to ground it in public domain...well, I'd like to think so at least haha.

I guess we'll have a whole new set of legal knots to work through. I mean as in Trademark vs. Public Domain Copyright. This does bring me to recall Southpark has frequently used Mickey Mouse in a parody fashion (as an evil, iron-fisted empire chief) and apparently did a good enough job of sticking to Fair Use that I can't find evidence Disney ever sued.

What I'm getting at is I do agree Disney is highly motivated to protect every bit of their IP to the fullest extent possible - no doubt their lawyers like this very much - but in a changing landscape, there may be certain workarounds that clever artists will use.