Until we have official confirmation, or a very well supported rumour, that AMD have secured all 3 GPUs next gen (or someone else), then nVidia are still technically not out of next gen yet. They are an option. At the moment though there's zero evidence pointing to an nV GPU in any console.
The same can be said for PowerVR as well. They are in Vita so there's still a chance that Sony could use a high end PVR part for PS4. Though in my eyes this is highly unlikely and AMD is probably the obvious choice. If PS4 is going to be a SoC and AMD is going to be the CPU side of it, I see no reason for them not to also have the GPU side of it too. It's reasonable to assume AMD has locked up all three (2 next gen, 1 current gen extender) consoles with their tech.