Sony don't need to do anything at all. You can lower the cost of more or less anything against its competitor in any market not just consoles and sales will go up. Firstly, Sony will wait and see what Microsofts stance is regarding price after the Xmas rush is over. If The Xbox goes back to normal price in January then you'd expect normality to be resumed in the PS4 starting to slightly outsell the Xbox again in America.
Lets not forget that the PS4 is trouncing the Xbox in way way more countries than its not (hence the current guess of 7 million more sales).
Sony I imagine would only start to contemplate changes if A: Microsoft introduced a permanent price drop and B: if that permanent price drop began to seriously impact sales of the PS4 over a continued period of time. Winning one month of the year in countries you can probably count on one hand does not mean disaster is looming now does it.
PREDICTIONS FOR END OF 2015: (Made Jan 1st 2015)
PS4 - 34M - XB1 - 21m - WII U -12M
