While eventually hardware will need to be upgraded "to keep up" the actual software stack is in the short run (talking 1-2 years) far more important.
Check out the Nokia tablet history, while N770 , N800 and N810 each are "upgrades" the actual difference in hardware did not make *that* much of a splash. ok, you can multi task a bit better and N810 has a (crappy) onboard GPS, nice.
But at the end it's the software stack that actually "makes" the device.
So I would think that the next "revision" would be a "minor" update (bit more ram or bit faster cpu if that can be implemented "cheaply") and will still be able to play "ball".
After all the difference between a "mid range" PC (700 euro / no screen) from now and 2 year ago is not that much (unless you are using it for high end gaming or workstation applications).
It might be now more Mhz, or more ram but the only thing that actually "eats" in that case the difference is XP vs Vista
The only "thread" would be a similar device that has far more power (while not eating battery's like a netbook) and even with access to OMAP4 that's still not such a "big" leap (besides a 4 instead a 3 on the box).