Ok, obligatory clarification here: I'm not campaigning for Barlog's new project to be based on an existing IP, nor the opposite.
All I'm saying is I can't know for sure, based on the information that is publicly released.
Barlog mentioned he was apparently going to pitch an idea towards Sony, but we don't know if he was successful. There are arguments on both sides to support whether it's a new IP or not.
Yes, Horizon was a major success but not all new IPs were as well received, like Knack orOrder 1886.
We can bet whether it's a new IP or not (and perhaps I'd bet in the same way you would), but the fact that we're betting means we don't know for sure. That's all that I meant.
Again if it was not a new IP, Cory barlog would not be at Sony Santa Monica. He quits Crystal Dynamics because they did not want to to do the "one shot" camera idea.
He is a creative and he will find another job if he is not satisfied. Same watch the postmortem of God of War, he needed to pitch the idea of a reboot of God of War to Sony. They wanted to stop the franchise. The problem they did a bad demo to Shuhei Yoshida doing the pitch and he was not happy but they decided to continue because Sony Santa Monica studio worked on two failures successively God of War Ascencion and the cancelled project. The second failure was the reason Sony Santa Monica stopped to help indie for development(for example Jouney was created with help of them). All the indie guys of Sony Santa Monica created Annapurna Interactive after this. If God of war reboot was a failure, the studio would have close. And this is the reason he cried when he saw the metacritic/opencritic reviews because he was under pressure. He didn't want to be the guy reponsible of Sony Santa Monica closure.
Sony knows they need to refresh ip, and create new one and it works well this generation with Horizon, Ghost of Tsushima and Days Gone was a commercial success too, it did not sold as much as bigger critical success but the game sold well. Same Naughty Dog is on a new IP too and closed the Naugthy Dog Uncharted cycle with Uncharted 4 and the Lost Legacy. It does not mean the franchise will disappear. Rehash the same franchise again and again only create franchise fatigue. Sony needs a mix of old ones and new ones. They have Uncharted, TLOU, God of War, Horizon, Ghost of Tsushima, maybe Days Gone, Ratchet and Clank, Spiderman for the moment, Astrobot, Sackboy, Dreams and Gran Turismo.
I am sure at 99.9% this is a new IP. All the usual suspect, some working in the industry seems to say this is a new IP. And I don't think Sony Santa Monica has valuable IP out of God of War(Kinetica..). If it is not a new IP, this is the next God of War.
EDIT: For The Order 1886, this is very difficult to do a huge upgrade of a game engine and do a game and at the same time and the studio grow to a much bigger team coming from doing PSP/PSvita game to PS4 games not easy too with new management process. This is probably the reason Sony Bend choose Unreal Engine 4 to do days Gone.
Knack is another problem, this is Japan Studio... And multiple creatives quit the studio recently...