I think the release order from these companies will be Nikon, Canon, Sony, with a small time difference between them. Sony Rumors are sure that the release of their next FF will be in 2012. Hope they release the 5DIII before the end of the world
I thought Sony announced a little while back that they're putting their main thrust behind their APS-C lineup (which most people see it as a retreat from the FF market).
If I remember correctly, they discontinued their Alpha-850 w/o replacement, leaving the Alpha-900 as the only available FF model (which predates the 850).