I also really liked the Lenovo concept. There was a lot of good in the model:
-bigger keyboard than with a slide out design
-"pure" tablet mode with keyboard folded back
-screen and keyboard are protected when device is folded the other way round

The two downsides that comes to mind are that opening it takes longer than just sliding out the keyboard on N810 and the keyboard might break if you keep it in a pocket folded to "tablet mode" a lot.

I think Nokia could create a device like this quite easily, as their E90 already has similar hinges.