You are assuming that burning information on one layer will not effect reading the other layers. I don't think we know that yet.
Well TDK has disc media which can go up to 200 gigabyte by putting multi layers on the Media:
TDK develops 2X, 100GB Blu-ray Disc prototype
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TDK Corp. has developed a prototype Blu-ray Disc that can store twice as much data, and record it at twice the speed, as existing Blu-ray Discs.
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To achieve the higher capacity, TDK added two additional recording layers to the disc to take it up to four layers. Blu-ray Disc stores 25GB on each recording layer and the standard currently includes single layer and dual layer versions.
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Well.. I assume all the time. And I'm not going to tell you where I work.
But really, I thought the whole point of the article was that HDDVD and Blue-ray could be printed on the same side of a disc. If the layers interfered it wouldn't be much of an invention.
we already have dual-layer DVD's and it works fine.