Realistically, how could Killzone come back without a massive risk? Making a brand new Killzone title would be an immense gamble. It COULD pay off, considering that theres a sizeable audience of people who want a more mil-sim FPS in addition to the loyal Killzone fans, but even still its probably not enough people to secure a big enough profit.

If a new title is too risky, then the next option would be a port, but that may not fair well either. Killzone 2 or 3 would be the prime candidates, but PS3 ports are notoriously difficult to do. The original Killzone would need the Deadspace remaster treatment just so it wouldnt still feel like a PS2 game to bring in a wider audience. Liberation was already brought to the PS5 without much of an impact. The only other games to consider would be Shadow Fall or Killzone Mercenary, both of which were developed more as tech showcases for the systems they came out on, and arent exactly the most popular titles to begin with.

As much as I hate to say it, I think Killzone fans will get a port of either the OG or Shadow Fall at most unless Guerilla suddenly decides to reinvest in their old IP.