I wonder if they are doing a semi early access thing here, where the season 1 costumes become available individually once the season 2 pass drops. Just as a way to pressure people to buy the Season Passes for early access, but this is all speculative bs on my part. The fact you can buy them individually on the xbox makes me think they have to do it for the PS4 and PC eventually, I mean there's a free to play version out there, and you want people to spend their money on your product, right?
More likely then not I think it will depend on the sales of the Season 1 pass, they will then compare those numbers to what they think they can get out of a Season 2 and then decide from there. SOOooooo earliest I would say is June.... but then again if you where to tell me the f2p version would drop 2 weeks after the initial release i'd call you crazy, so what do i know?