At first I thought it was just hiring to help complete Days Gone but clearly it isn't. Days Gone must be close to completion or at least in the polishing stages:

Sony Bend Studio, the creator of Days Gone, Syphon Filter and Uncharted: Golden Abyss, is looking for top talent to join our in passionate team in creating a new AAA PlayStation 4 exclusive.

We are seeking a Senior Staff Gameplay Programmer to contribute to our development process. This position specializes in specific areas of programming that centers around the architecture and implementation of game engine code systems used for the creation and development of a game application.

https://boards.greenhouse.io/sonyinteractiveentertainmentplaystation/jobs/660557#.WuwIZaQvypo

Sony arnt gonna let up on the exclusives front.... and thank goodness for that.

Another prove PS5 will not be release in  2020 or even 2019. Probably a cross gen title or it will be a PS5 title, but the games will take more then 3 years to make. 

They will always keep delivering , and never satisfied with one popular IP.  Sony Interactive Entertainment  are monster and in full throttle . Xbox will not able to beat them in this gen , never . Because they have the mentality of winner and mentality of gamer. 

Thats fantastic !!! Thanks, Sony :)

I don't think it's proof at all. Most people think (as do I) that the PS5 will have backward compatibility. 

I'm not a specialist... Is it possible to know more about the progress of the development from the ad?

Depending on this, it could release in less than 3 years. They clearly have 2 different teams, and the second one could have made some progress already. Could be one of the last PS4 exclusives, like TLOU or GoW Ascension for the PS3.

PlayStation never release an exclusive first party  title on older platform. If it's a year before release or in the same year on PS5 release it's still possible. 

Sony also never released a midgen hardware update either, but reason for not releasing the title on previous platform was different architecture, the game are being developed with two systems in mind Pro and Base, with PS5 having same architecture its pretty safe to assume that all the title in development will be  forward compatible. I think first gen PS5 games will all be backward compatible, then slowly phase out the base PS4. and phase out ps4 pro when PS5 pro launches.

The only surprise here is that they expect to finish this new AAA exclusive in time for a PS4 release.