Well, I seem to have lost my N810 to my missus, who is using it a lot to read pdf's etc. on flight/train journeys.
I think if nokia does decide to reduce the screen size, they will lose a lot of customers.
Certainly the only reason my wife has the N810 is so I can get the new one (whenever it comes out!).
It all depends on the device's usability at the end of the day.

Maybe a smaller screen will make it unusable, or maybe a combination of auto rotation for pdf viewing, etc. may make it smaller and easier to use?
Surely nokia will have thought this through in the design?

It's difficult to comment without any hardware to make a judgement on.
I think it's going to be a combination of disappointment and amazement, but given the amount of waiting and hype we have had for it I guess that's to be expected.
I suppose a holographic display is out of the question ;-)