IMO the best that can happen is that when a process shrink will be available, within the same TDP they may increase clocks a bit
In previous years what the console makers have done is (a.) reduce the cost of the console, (b.) reduce the size of the console or both when a die-shrink is available.
Personally I have a strong suspicion that MS will boost the GPU component of the APU in the X-Bone by a large margin (50%) when the die-shrink is available, if I am right then that information will likely be leaked many months ahead of the die-shrink as the developers will of course be notified in advance so that they have the time to modify their upcoming games and catch up with the serious graphics performance advantage that the PS4 has over the X-Bone.
The large amount of SRAM on the X-Bone APU will benefit a great deal from a die shrink relative to other parts of the APU's anatomy which would help MS quite a lot if they decide to keep their APU identical at which point they would benefit (a little) more than Sony from a die-shrink.
Whether that happens or not there would be no benefit for Sony to do the same thing and they could simply pass on all (or at least some) of the cost savings to their customers, if so this could mean a large cost difference between the two consoles in the future, albeit there is also an extra set of equipment provided with the X-Bone.
The other thing that's important with regards to the future costs of these two consoles is the RAM which both have in abundance, I personally don't know what the relative cost differences are or whether the cost of the RAM will go up/down relative to the other as time goes on.