I mean, given that Disney wasn't doing anything new with Roger Rabbit, I'm glad he got the rights back. But I think part of the reason that very little new material got produced is that the first movie was kind of lightning in a bottle. It's possible other production companies would have had to be involved to get something new done, depending on how the rights were parceled out. (We're all talking about Disney here because that's who Doctorow focused on, but it was a co-production with Spielberg's Amblin Entertainment.) And I think you're right that he's unlikely to have the rights to do a sequel that's too close to the original.
Yeah, isn't that the central gag of the movie though?
Not to mention some of the actors have passed like Paul Reuben who really sold the cartoon aspect of Roger Rabbit.
https://www.youtube.com/watch?v=rDKfLZNMtmU
Paul Reubens wasn't great. With the right direction he could easily have been as good as Fleischer, but I'm sure he was (incorrectly in this case) trying to show he could be less over the top than Pee Wee Herman, who was a known quantity in LA at that time.
What fascinated me is how I reacted to the Jessica Rabbit pencil test, where she snuggles up to the live actor. Even in that low resolution, lousy video transfer, I had a visceral reaction to her character. Those animators were all kinds of good even for a minor demo.
often big media companies aren't interested in exploiting specific properties if there is ongoing litigation regarding them.