It will make it sell a lot for sure, but I still don´t know if it will sell more than the PS4, after all, PSPLUS gives 5-9 free games for the new Ps4 owner, namely, the ones I have got last week when I bought mine:
1 - Don´t starve,
2 - Rezogun,
3 - DC Universe,
4 - Blacklight,
5- Outlast,
6 - Warframe,
7 - Zen Pinball.
Some people got contrast too for free.
That said, as a Xbox One owner myself, it makes me happy to see the install base increase, since it can lead to cool exclusive games.
But, overall, the PS4 is still the better deal.