Open-source software works because any of us can download, revise, build, and test the product in our own homes. You can execute your own design revisions.
Hardware doesn't work like that, unless it's made of a handful of hand-soldered parts, and even then the results tend to be more functional than beautiful, and they suffer from lots of quality-control variation.
So, no. The best you can realistically hope for is for something like the Chumby: Designed by a core team, who sells it to defray the manufacturing and development costs but gives you all the schematics and software and encourages you to hack it.
Meanwhile, large companies have spent millions of dollars to compete with iPod and failed, so you're not exactly setting your sights low.