I mean, act 2 isn't done. There's going to be a third act, while smaller than act 2 it is going to be somewhat story packed.
And of course the epilogue.
Arc says 1 or 2 years in his "how much longer you think you'll keep working on the game" but I also heard that about a year ago.
It's hard to put an accurate estimate on how long things would take.
Especially if you have a lot of people asking for more side stuff.