Sony has Bungie now, one of the best FPS developers of all time, who are currently running one of the most popular FPS of all time, do something with that if they're so concerned and then make the next Bungie title exclusive to PlayStation. Bring back Killzone and release it in a year without CoD since CoD is moving to a 2-year release schedule now, which gives other companies a chance to grow their FPS franchises.
All this panic over one dang IP. Sony will still have plenty of FPS choices, including CoD which will remain multiplatform, plenty of M-Rated titles like CoD to appeal to those same audiences, a domination in the Action-Adventure genre which is proving to be very popular looking at the sales of God of War, Last of Us, Horizon, etc. And an opportunity to create their own set of FPS franchises, all whilst CoD will remain multiplatform and go onto a 2-year schedule, Lol.
If your entire business relies on one single IP then that's on you (we know it doesn't though, Sony will be fine without CoD and likely still outsell Xbox, Lol). Xbox was already known as the "Shooter-Box" once before and that was when competition was at its peak and all 3 companies were doing amazing.