Seems like the new IP will have major focus on online gameplay and co-op gameplay as Guerrilla games have listed the below for hiring:
We’re looking for regular/senior designers with online, multiplayer or coop experience to work on our unannounced new IP. You’ll be part of a small team tasked with creating groundbreaking, innovative online gameplay.
Read more at http://www.worldsfactory.net/2014/05/05/guerrillas-new-ip-to-have-significant-online-focus#GakfyTT9gyWFc9kA.99
Guess take it a rumor for now but An Insider has leaked a little info that Guerrilla Games next game will be a completely new IP for the PlayStation 4 ( making it the second PS4 game from the studio after they released Killzone: Shadow Fall which went on to sell over 2 million ) and that the studio is gearing up to announce it next month at Sony's conference at E3
This is the same person who leaked the PS4's UI and features in the past as well as PS4's 1.70 update
While im sure everyone already knew that the studio was already working on a different title other than killzone its interesting that the next game will be revealed very soon.
imo please no more FPS's thanks!