There are watches today that are 100x more powerful than Macs of that era. Almost anything that was good in a file format from that era would be bad today. Every novel and innovative application feature from Photoshop 1.0 would be seen today as trivial. Many of today's features would have been inconceivable.
If you think you can do better, then I'd encourage you to try. Just start shipping an app with a file format today, get a lot of users, take it through 15 major versions [2], and come back to us in 25 years. Then you can lecture those of us left alive on the right way to do file formats.
[1] http://en.wikipedia.org/wiki/Macintosh_SE [2] http://en.wikipedia.org/wiki/Adobe_Photoshop_version_history