More 3DI should have mentioned this yesterday, but there have primarily been two reasons why the parallax techology Toshiba is using in their 21" autostereoscopic display was previously considered unusable in larger screens. First, the viewing angle is severely compromised unless you're in the "sweet spot," and the sweet spot is very small. However, producing nine images (the number in the 21" display) is going to significantly improve the viewing angle (because you only need two for the 3D effect, if I'm understanding it correctly)--in essence, everything above two images is increasing the size of the sweet spot.
Second, parallax displays previously had resolution issues. Daily Tech had an article today that mentions Toshiba using a "low-temperature poly-silicon technology" to resolve that problem. Plus, this tech also allows the production of a panel that has brightness levels comparable to 2D panels.
This is pretty damned exciting technology.