Whatever happened to the original backstory for the land? It reads as follows, and I quote:
Of course, everyone knows that Mickey's Toontown existed long before Disneyland was built right next door. One happy day in 1952, while Walt Disney was in Toontown visiting his pal Mickey Mouse, his dream for a new park come up in conversation. Mickey knew that whenever Walt got that sparkle in his eye, whatever he was dreaming up was bound to come true. So he was dismayed when Walt confided in him that he was having a difficult time finding a site large enough to accommodate all the wonderful things he had in mind.
"Oh, boy, I've got a swell idea!" Mickey exclaimed as he grabbed Walt by the hand and led him over to the fence that separated Toontown from the human world. "Take a look over this fence," continued Mickey. "There's a fine and dandy parcel of land just on the other side that would be a wonderful place to build Disneyland!" And it was.
Many years went by before it finally dawned on the toons (the first time something dawned on them besides a happy cartoon sun) that since it was so easy for them to go next door to visit all their non-toon friends at Disneyland, their non-toon friends could just as easily come visit them in Toontown! And that is exactly what happened when Mickey's Toontown was "finally" opened to Disneyland visitors in February, 1993.
So I really want to think that Toontown actually exists because of Mickey. Let's not forget that Toontown is actually an outgrowth of Mickey's Birthdayland/Starland, which debuted shortly before the release of "Who Framed Roger Rabbit" and which was themed primarily around Duckburg ("DuckTales" had just debuted a few months prior).
And let's also not forget that Mickey's Toontown Fair, which replaced Mickey's Starland, has the exact same toon-like style as the regular Toontown, but Roger Rabbit was nowhere to be found there. Also, I like to think that the Mickey cartoons of the 2010s (which is what Runaway Railway is obviously themed to) have a bit of Toontown vibe to it.