As far as I know the 900 won’t be able to use windows 8. I have one and from all I heard we won’t get 8.
Anyone using the 900 found a flash player yet?
It won’t because Windows 8 was designed to use hardware that the Lumia’s don’t have, so even if the Lumia’s 900, 800, 710, 610, could receive Windows 8, there would be no benefit.
But they do plan on releasing an upgrade to the current Lumias as far as they can go.