I found this article the other day and have been meaning to post it. I'm not sure if this is the right place, but the article does talk a bit about what was to become of Casey Jr.
The article is about how since the 1930s, Disney has wanted to do something involving the Wonderful Wizard of Oz. It talks about how a movie was planned but abandoned, how Casey Jr. was to be turned into a Candy Mountain/Oz dark ride, and the troubles surrounding the Return to Oz movie.
I thought the article was very interesting, I hope you do too.
Jim Hill : Disney's long, long journey to Oz
And this is the clip of the Mickey Mouse Club episode when the Mousketeers where actually going to make an Oz movie:
YouTube - The Rainbow Road To Oz
Here's a question for all you armchair imagineers: How would you bring the land of Oz and Disney together?