Yet, Nokia actually has a good track record, overall, of doing exactly that. Just look at what they've got out in the world right now, in terms of form factors:

• flip phones
• E(50?) type candybars (with number-pad and trackpad on the face)
• E66 type candybar sliders (with trackpad on the face)
• E71 type candybars with half-screen/half-qwerty faces
• E90 type micro-laptops with a candybar outside
• Soon, E75 type side-slide qwerty with candybar type face
• Soon, the Tube, touch screen with no number bad nor qwerty (not sure about the d-pad).

That's a pretty good list. And they support them quite well. Though, personally, I wish the E75 had a full screen face instead of half-screen/half-number pad.

But, I was just looking at this new Fujitsu concept (here and here) and thinking it'd be an interesting direction.

1. Start with the N810, remove the buttons from the face (and maybe some other cosmetic things like removing the bezel and making a flat face).
2. Remove the slide-out keyboard, and use that savings to make the device thinner.
3. Make an attachable QWERTY keyboard like the Fujitusu concept has, but make sure it's durable and can attach solidly.
4. On the second page, the picture also shows what could be a game-pad attachment.
5. You could also make an attachment that's a docking-station/charger-bay for it, to which you'd also attach USB devices

If you could pull of a sturdy version of that design, you'd have the base design that would force developers to think in terms of touch screen and tablet, while also allowing users who prefer a keyboard to buy such an attachment. The game-pad attachment could further make the gaming crowd happy, and the docking station would be useful for those who want things like external storage, full size keyboards, maybe even external displays. Depending on the details of the attachment interface, it might also be possible to make things like external storage attachments (either extra SD slots or SSDs), especially if you can daisey chain them, and make part of it wrap around to the back.

(if the attachments were somehow reversible, you could make storage devices that wrap around to the back also function as face covers, and have the keyboard attachment combine with the gamepad attachment)

(and, if you do that, please make a keyboard with the layout of the E90, and the feel of the E71 ... )

I think that'd be an interesting way to address all of the various crowds. I don't know if it'd be practically realizable, but I'd still find it an interesting thing to research.