Honestly at this point I don't want another Killzone for a long time, and I want them to pretend that the ShadowFall timeline never happened. Then next gen, just reboot the franchise.
That leaves room for a Killzone 2/3 remaster! Put them on 1 disc fully remade for the PS4 with a MP component that combines the maps and weapons from both games! Oh and add 4 player co-op to both as well.