The World-e levels certainly exist. They're not like super bad-bad but their whole "borrow enemies/items/etc. from other Marios" gimmick has been done so much better in so many fan projects. :P
I think raocow put it pretty well in the last episode of his LP of these levels: "it's kinda funny to think that if nintendo was in the business of doing rom hacks, they'd be pretty bad at it. like this is a bottom-tier rom hack experience. but it's interesting because it's official."
This is basically DLC, but instead using a physical peripheral that isn't the cheapest. Kind of a hard sell. Its failure is pretty unsurprising.
I wonder how many plans there were for potential future levels that got canceled. TCRF says that the World-e castle has a 2nd and 3rd floor accessible if you have 9 or 17 e-Coins respectively, but you can only get 8 with the released levels. And so many never even left Japan, only 3 e-Coins were originally available in the US.
Anyway, the levels are nothing extraordinary but getting all the Advance and e- coins is where the *real* challenge here lies.
Zeal