The ESRB's website is usually good for a few leaks a month, and it looks like it's starting off 2012 true to form. A NeoGaf user user exploring the website found that the listing for the original PlayStation 2 Killzone game had been updated to include PlayStation 3 as a platform. Since the ESRB doesn't re-rate games for new consoles simply because they're backwards compatible, this likely means that Sony is preparing to announce that the original Killzone is coming to the PlayStation 3, in one iteration or another.
There are a number of different ways Guerrilla's shooter could be brought to the PlayStation 3. Odds are it won't be a full-fledged HD remake akin to Shadow of the Colossus or God of War, simply because it wasn't as popular as those games were, and Sony doesn't need to promote the Killzone brand anymore than they already have. Killzone 2 and 3 are already out - if anyone wants to become familiarized with the brand they'd likely start there, not with the PS2 original.
And, well... it's not really as good as the PlayStation 3 sequels, so it might not be worth Sony or Guerrilla's the time to completely remake it. Odds are this updated listing is referencing a slightly upscaled remake for the PlayStation Network or simply a PSN version of the original with no changes at all. We've followed up with Sony to find out if they've any comment on this story, and we'll be sure to fill you in as soon as we hear back.
Update: Sony has confirmed that a port of the PS2 original is coming to PSN on January 24 and will cost $9.99.