If you would make such a thing you would automatically have to compete with thousands and thousands of hardware pieces currently on the market. The Pandora almost has no direct competitors at all in its current form. I have no doubt that it will be a little commercial success. However, a Pandora Box would be something totally different.
With a little research and common sense you can build such a thing yourself for about €250 to €300. And then you would have something pretty cool, in x86 form. You would have the ability to use it as a Home Server, an Open Source gaming machine, Media Center, or an emulator machine. There is tons of (free) content out there for these kinds of devices. Something like a Pandora Box would eventually have some buyers, but I don't reckon very many. Maybe you're better off buying a Beagle Board and building it into a little case (which you could also make yourself for a few Gil). This will cost you about $175.
As said before, it has to compete with a LOT of other hardware out there. You need to specifically need to target people that are not willing to do the research and building of these kind of devices. Offer them an opportunity. It needs to have something that any other device doesn't have, else it'll fail.
The Pandora has this thing that other machines don't have. It's portable, has a nice screen, full keyboard, gaming controls, it will have much free content, etc. I don't know any other device that comes at this price, with such possibilities.
Together with a nice marketing campaign you could maybe pull off something like an Open Source video game console for big screen TVs.