A bigger screen, e.g. 4.1" as in the N810. The overall device could still be smaller than the N810, which would be pocketable for many users.

It doesn't need to have a physical keyboard, but if it has a keyboard it should be a good one. The HTC Touch 2 Pro keyboard is getting very positive reviews. It HTC can do it, so can Nokia. It ain't gonna happen though, because Nokia has said they want to standardise user expectations for Nokia keyboards around what is offered by the N900 and N97 mini.

A bigger battery. If I can browse the web solidly for four hours, or if I can capture a GPS trace from a one-day hike, then I'll be happy.

Roger