Given where the car mags price the IS350, I suspect that an IS460 would be in excess of 50K. I don't think Toyota can make a business case for bringing such a car to market. A few one-offs for the autoshow circuit will likely be the last of this, much like the much talked about Rod Millen IS430.
Seriously, Car and Driver got the IS350 to 60mph in ~5 seconds, Road and Track said the skidpad was limited to .80g because of VDIM. So unless LEXUS rewrites the book for VDIM, I don't see enough buyers willing to pay the premium for increased acceration that is all-but unusable on the street anyway. A performance hybrid would fit the current Lexus lineup better.