blu-ray will probably go down the multi layer path soon. We could see 4 layers or even 6 layers disc soon.
check this quote from Wikipedia:
In December 2008, Pioneer Corporation unveiled a 400 GB Blu-ray Disc (containing 16 data layers, 25 GB each) that will be compatible with current players after a firmware update. Its planned launch is in the 2009–10 time frame for ROM and 2010–13 for rewritable discs. Ongoing development is under way to create a 1 TB Blu-ray Disc as soon as 2013.[101]
Multi layered discs will require higher powered lasers, as they would have to penetrate deeper into the disc. But then again, perhaps multi layered discs may not be writable with home computer equipment.