Well they're going to at least wait until all of the combat fixes are done, I think (based off of info given in Letters from the Producer) that these will be finished by the end of June. I believe the goal was 2 months but then given the downtime I think the end of June is a reasonable time frame.
After that I think their best course of action would be to release with the first expansion. This way that gives PS3 players even more incentive to jump in right away, especially since we'll likely get new classes at that point so everyone will be leveling low rank stuff including the veteran PC players.
Not to mention over the course of time between now and then they'll be adding more side-quests, dungeons, hopefully instances and whatnot. At that point FFXIV will have more than enough content to reasonably launch on the PS3. I'm estimating September, the 1 year anniversary of FFXIV's launch. This will put it a bit ahead of all the huge holiday season titles but still at about the point where sales could be increased by it.
If I recall correctly, that was the strategy with FFXI's NA launch right?