I've been doing some tests with VB Wario Land (thanks to Captain Drake for arousing my curiosity) and it really would be a bitch to map.
I've been trying to map the first stage using the right view (since there are two views, one for each eye) and without any layer disabling it's really long and time-consuming (no layers in this version; there's apparently a debug build that the author keeps for himself where you can cycle through the various foreground and background stage elements). You basically have to remove all the sprites and the background by hand. Now that wasn't too hard in the first level, but the second already has at least 2 layers in the background instead of one.
There's also the question of what to do with the parallax background seeing as Wario can jump into it at several points, but because it doesn't scroll at the same speed you can't align the jump points together. Basically what Captain Drake said earlier. I'll try to thinker with it a bit more for fun, to see how it might be done best in case someone else decides to pursue this.
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"With the first link, the chain is forged. The first speech censored, the first thought forbidden, the first freedom denied, chains us all irrevocably." [...] The first time any man's freedom is trodden on, we're all damaged. - Captain Jean-Luc Picard
B*tch, meet reality. Reality, meet b*tch. - Me
