Logically thinking... if Nvidia was to stay within the voltage standard, they would not be able to pair up two 480's or 470's or 465's without crippling them quite a bit and since the 460's would not need to be crippled as much (if any) they would be the suitable canidates but again, i am just thinking out loud, i don't believe anything these days till i see it.
My only problem with 460's being used for a 495 would be that 2 x GTX 460's in SLI would not edge out the 5970 and i don't think Nvidia is about to issue a dual-GPU card that does not take top crown.
My guess is that Nvidia has something up their sleeve, they always do.