There are two things confirmed as of right now: 1. The next 4-5 weeks will be Part 1 Flashbacks/Filler episodes, and 2. They are going to animate every light novel released, starting with Sasuke's novel.
They have yet to animate chapter 699/700, so that's going to happen at some point. They also have the Naruto Gaiden chapters to animate, which will also happen as it is canon material.
From this we can asses that they will do something similar to what they did back in Part 1 - which if you don't recall, they placed multiple seasons of filler content inbetween the last two chapters of part 1 in order to fluff up the material. In this case, I suspect they will use filler content to fluff up the material in the timeskip between 699-700. After all that (years of filler material, the light novels, and the Naruto Gaiden), the Boruto manga should have enough material for them to animate 699/700, the Gaiden, and then work on the Boruto manga adaptation. Since the first 6-8 chapters of the Boruto manga are recap of the Boruto movie, I would also assume that they will be pulling a DragonBall Super and reinterpret the Boruto movie as well.
