ZFS: If I understand correctly, pooled storage can (will?) look like one volume. This holds the possibility of NAND storage for the operating system pooled with the hard drive storage that appears to the user as one volume.
This approach would minimize the need for the more expensive flash storage and capitalizing on instant-on / resume strategies that NAND storage offers. The cost factor of NAND storage for OS / Cache could possibly make implimentation more feasible on an earlier timeline than replicating the entire hard drive / eliminating the conventional hard drive.
Leopard - What We Know & What We Can Expect