At least that's according to a Kotaku preview, which contains the following snippet:
"Sony won't go into specifics yet, but the game's producer told me that multiplayer is getting an "overhaul," with details set to be revealed at next month's Gamescom in Germany. I asked about the possibility for co-op play, especially considering the inclusion of that co-op style healing move I described above. The producer again directed me to Gamescom, though I did not take that to be confirmation that the game would have co-op, just that we'll know one way or the other soon."
Mark your calendars then, folks. GamesCom it is. We really liked how fresh Killzone 2's multiplayer felt compared to other shooters on the market, but found it a bit tedious at times. There was clearly something a little bit genius about the game's constantly rotating mission objectives however. We can't wait to hear more.