Can it? Yes. Will it? Only if the NX is a truly massive failure.
Let's say the Xbox One ends up this generation somewhere around 40-50m. The Wii U will be around 14m. That's already 54-64m; making the PS4 need to reach 108-128m to keep its 50% marketshare.
Now, let's say the NX turns out to be a bigger flop than the GameCube and sells only 20m. That would represent a toal of 74-84m; making the PS4 need to reach 148-168m.
You see, even if the NX flops, it will be very hard... unless you think the PS4 will surely outsell the PS2.
That applies only if you include the Wii U into it. Including the Wii U into the marketshare(once the NX is officially released) makes as much sense as including the PS3 into the marketshare in my opinion