FF13 released December 2009, -2 released December 2011, -3 released November 2013.
There is no reason in my mind to expect Part 2 any sooner then two years, and given the switch to PS5 in that time frame, there may or may not be a PS4 release.
I think two things to consider are 1) SE seems to be functioning much better now than they did back then, and 2) they're using Unreal Engine now vs their own proprietary engine back then. They've already laid a lot of the groundwork in FF7R so I think that the 2nd installment will likely pick up a large portion of the game.
Whatever the case, I'm in the final 3 chapters of the game, really hoping it keeps up. It's been great so far.