I could be wrong but I think it's a bit early to expect a new tablet already.

Here's the release schedule of previous tablets so you see what I mean:

Late 2005: Nokia 770
Early 2007: Nokia N800
Late 2007: Nokia N810

In other words there seems to be a gap of about one year between tablets. The N810 only arrived a few months ago.

What MIGHT happen is we get a variation on the N810 which uses Wimax, but that would probably be pretty much the same tablet otherwise.