So far with the famous Mikcey and co characters we have had worlds such as Disney Castle, Disney Town, Timeless River (based on the Steam Willie Shorts) Symphony of Sorcery (Based on the Fantasia shorts of 1940) and Country of the Musketeers (with Micky, Donald and Goofy as Musketeers in 2004 film)

 

But the Mikcey Mouse from Mickey and the Bean Stalk from Fun and Fancy free could be another world of Mickey's Past. Or will Kingdom Hearts 3 do with out the worlds of the past idea.?

It would've fit more if it was in Dream Drop Distance though...but I doubt that there will be time now for such worlds.

That would have worked for Dream Drop Distance or Birth by Sleep, but we're past that point now. It would make more sense to visit worlds that wouldn't suggest Mickey's past.