Besides Napoleon and Cinerama, the widest aspect ratio that should be on DVD is 2.55:1.
The Ultra Panavision films such as Ben-Hur and The Greatest Story Ever Told were never meant to be projected at 2.76:1, despite the full negative image being that. Cinerama is 2.59:1, with a curve.
Here's what Cinerama and Napoleon's tryptich would look like in 16x9:
While Napoleon won't look as spectacular, Cinerama could be stunning if transferred well to DVD. I read that doing the smilebox process in 16x9 is possible, so it would be neat if it was done in HD. Then, the 6-channel Cinerama sound could be converted into a wonderful 5.0 mix. It's not anything like seeing it at a Cinerama theater, but it could still look great.