Sony probably wont need to do anything. By the time summer is over you would expect that the PS4 will be over the 50% market share and so what if it loses traction during the holiday period. It hasn't stopped it winning every week since the turn of the year has it, and comfortably I might add. The multiplats will drive sales over the winter and the fact that Uncharted has moved into 2016 won't really make that much of a difference. People that are planning to get a PS4 in Winter 2015 are probably going to do it, Uncharted or not.
Its selling at over 2:1 over its nearest rival and that doesn't look like changing any over the next few months. In fact, it will probably be even higher with Bloodborne on the horizon. I don't think Sony will be bothered about losing perhaps 2 months of the year, when they are creaming the competition for the other 10 months.
PREDICTIONS FOR END OF 2015: (Made Jan 1st 2015)
PS4 - 34M - XB1 - 21m - WII U -12M
