It's unlikely they will be dropping it before 4.0 and it seems unlikely it will be dropped on 4.0. even if we assume that the PS3 is the absolute lowest and weakest system, it is still a sizable portion of the player base. even if PS3 players are (and i am completely making these numbers up) just 10% of the player base, SE will be taking a huge risk that i don't think they would want to take. that's a chance SE could "potentially" permanently get rid of 10% of its players. having less players means less subscription which means having money from the game. from a business standpoint (and video games are a buissnes so they want to make money) that's a lot of money your throwing not gonna get. i am not arguing if they should or should not or even if it is holding back on major aspects of the game. so long as players are playing on PS3, it is very likely not gonna be dropped.

TL;DR: Square Enix is a business and businesses need to make money, so they won't drop PS3 so long as it is even somewhat profitable.