Lemme calculate it out
Gaiden will take approx. 1 month to finish, 4-5 episodes, maybe even longer. Max 7.
Mitsuki Gaiden maybe? 1-2 episodes.
Boruto Movie rehash will take another month to finish.
Then they gotta animate the Shojoji/Mujina arc. Another month or so to finish.
By the time they reach the Shojoji arc, if my calc. is correct, the Manga will have 3-4 (or more) chapters. At least one more arc or so before they "completely" catch up.
We have a good year or so before we have to worry about it. By that time we don't know if the anime will go on hiatus or not.