I don't care about wimax, because it isn't available were I live.

I think nokia should improve/perfect the usability of the internet tablet, making it a web tablet with a desktop/laptop quality browsing experience.

-full speed flash support: n800 is too slow for some flash heavy sites (high bitrate video for example)
-embedded video support (windows media, quicktime and real )
-full speed for Ajax heavy sites (google docs, reader etc. etc.)
-should be perfectly stable: both Opera and the Mozilla browser aren't perfectly stable. (sometimes they crash: NOT acceptable )
-fully usable with your fingers: using software improvements and maybe a better touchscreen (multitouch??)
-better outside usability : the screen of the N800 isn't viewable in bright sunlight, so a better screen that solves this would be welcome.
-improvements in the text input methods: like a hardware keyboard, or working hand writing recognition, or other software input methods (trace writing, better error detection in words, a d-pad input method etc.)
-bring back the Nokia 770 hard cover: it worked SO well, and protected the device perfectly.

Adding other features aren't necessary in my opinion:
-GPS navigation
-slick looking UI with zoom effects (like the iphone)
-better camera
-stereo blue tooth headphone support

they could be nice, but the MAIN feature of the tablets aren't fully mature yet and should be the top most priority.