990 Jinbe- 999 Luffy, 1000 new nakama
Or like many said, it could be the match-ups becoming obvious.
Maybe looking too much into it but it should be Strawhat related if they are counting down the Strawhats.
Or it is just convenient that there is currently 10 Strawhats.
I think it is a bit too soon to have a new crew member. The real fights have not even started
–- Update From New Post Merge ---
You don't believe we could get 10 more chapters this year? Oda would still be able to take 4 weeks off and have the Christmas break and it could still happen. True, it is not extremely likely, but I think it could happen.
For me it would really suck if the chapter is released during the end of year festivities. Christmas is a family event that I cannot miss but nobody reads One Piece in my family