At this point I think you would need to manage the device from start to finish.
Basically put out limited line like Apple. Use high quality and standard chipset. I mean like a good ethernet chip, a good sound card, etc. With a standard build it is way easier to test your OS and make sure everything functions on your various models.
From there take Gnome or KDE and fork it. Go the Linux Mint Gnome route. If you are a company you can just decide how things work. Macs work one way, Windows another, but for the most part they work the way their company's wants to. That standard is what makes them popular, even amongst developer types and the kind of people that go to OSCon.
Then get a good testing community going. Make sure it works with printers. Make sure it works with projectors, make sure it works with dual monitors, make sure it works with the keyboards.
Come out with your own damn keyboards and mice.
Make the upgrade process simple, straightfoward, and automated. Certainly use a package manager, but hide it away.
The community might be able to take it and abstract, but given the linux community they would just tweak it to the point where it isn't as "beautiful".
Ubuntu tried and failed many of things. I think mostly because the people who generally run linux do so because they want to.
The difference here is that someone will walk into best buy, login to amazon, or your own site, maybe a dedicated store (think apple store) and walk out with a device that runs an OS which happens Linux...not buy some hardware and "try" to get linux working on it.
I don't think HP, Dell, etc have any interest in this and so someone needs to start it. Maybe we can leverage open hardware, maybe not, but I think we need to replicate the Apple model.
From there the hard part. Get the gaming community behind you, get Office to run on it...I mean the real Office, and keep going to get the world to treat your product with respect.