1) Multi touch screen that works with a passive stylus (I do not care if this is capacitive, resistive, or unicornium)
2) AGPS, Compass, Gyroscope
3) Tegra 2 (or at least dual core ARM anything, with an nvidia graphics package, so we'll get vdpau - which means mplayer et all will Just Work with acceleration)
4) 1GB RAM + 8 hours active use battery. RAM and battery life are pretty intrinsicly linked, so one may have to compromise the other - battery wins I reckon.
5) 720p screen + 8 hours active use battery. Video and battery are linked of course too
6) A *good* pdf reader. Goddamn it.
7) 32GB internal, 64GB SD
8) Bluetooth, wifi n, 3G (and can be networked for 24 hours without compromising the 8 hour active use wish above - ie I want my IM availability to be "Online" if the tablet is turned on)
9) Open hardware. So we can install Android on it without the nitdroid team having such a battle. And install Windows-ARM on it should we be stupid enough. Open you hear me? Everything submitted upstream to Linus.
9) Dual cameras.
10) An email client that covers the basics - multiple identities, multiple or merged inboxes, per-folder optional notifications, imap-idle
11) Flash
12) etc