What you are describing could look like a drafting board or an interactive coffee table. You can build one now. Just buy a LCD TV of suitable size and multi-touch bezel from AliBaba. The bezels have USB interface and mimic a mouse.

The main problem I see is that instead of touch, I'd much rather have pens, etc. Like the Wacom LCD tablets - but BIGGER!

I agree with this. When you get to a certain size, while fingers work, pens are much better because the system will placed on a table. Fingers on a touchscreen of certain size will probably stick within the kiosk realm, or game. You can do some typing, but you're largely looking down.

A very large touchscreen PC with sufficient horsepower could be good for drafting, autocad, or maybe solidworks. Things of that nature where you're designing and creating.

Some 20" and 27" tablets were shown at CES. Large tablets are inevitably too heavy to hold in your hands or rest in your lap, so I think separating the display from the rest of the PC Cintiq-style makes sense. And you can have a Cintiq today.

Its also possible to use a big screen low spec tablet and use it as a "termial" with VNC or something, connected to a high spec PC.

I'm imagining it and it is melting.

Sure, in a few years.

We're almost there. When batteries and chips made out of Graphene go into production, we can have <3" supercomputers.

The only limiting factor is the OS and input devices. Android is bad as Operating System for productive usage, because it's made for consumers.

Silicene > Graphene.

When we start better understanding how self-organizing structures work, we'll be very close to build miniature mobile supercomputers with extremely low energy consumption. I guess the battery and chip will be made out of the same material, but different structures. Production will be very cheap, because manufacturing will not require lasers, toxic acids and rare materials anymore.