my view, and some will argue and say it was never the plan is
it was meant to be a year with season 3 coming in end 2016
however it has been delayed somewhat.... so now, who knows, My guess is DLC #2 will come in the middle of this year...
i say DLC #2 because there are hints that season 2 was not received so well and DLC2 may do something different.
if i had a gun to my head and had to bet, i think DLC #2 will release in a far more complete state, with only small content updates over the proceeding year, with most patches being tweaks and fixes.
my thinking behind this is, horizons launched very bare bones and some would argue that by the time a lot of the "good stuff" game, the season pass had been discounted heavily, therefore, if FD did the same again, the risk is people would just wait until 3.2 or 3.3, get more content AND get it for a bargain price.
releasing a largely complete DLC however means most will (hopefully) not have the willpower to wait and will jump on it at full price.
but this is all my pie in the sky conjecture.
2.4 i reckon will probably launch at the same time as DLC #2 (or season 3 if you want to call it that for now)