Engadget has an article shows a concept that looks like a cross between the Tube and the E90, that was shown as part of the Tube's webcast.

I'd buy that concept, if:

1) T-Mobile-USA 3G
2) GSM Voice, SMS/MMS
3) Maemo (with Android extensions and N-Gage support being nice add-ons)
4) S60 PIM apps ported to it (integrated contacts, calendar/todo/tasks, bookmarks)
4) standard 3.5mm headset jack
5) micro-USB with easy to select/change client/host/otg modes
6) SyncML for contacts, calendar/todo/tasks, bookmarks
7) decent portrait camera, with flash, and video support
8) would be nice: micro-DVI with DVI-I
9) obviously bluetooth (with DUN, PAN, HID, and BIP) and wifi (usable both as a joikuspot type access point, and as a client)

I think that'd just about be the perfect tablet.