Prediction:
final volume will be 120
adds up because pre timeskip had 60 volumes and 600 chapters
so if post timeskip is the second HALF of the story then it should be 60 more volumes and 600 more chapters.
with this, the final chapter will be around 1200~
each year has 48 weeks and every week we have a chapter, but if we assume Oda takes a break at least once every month then thats 36 chapters a year
36 chapters x 3 years = 108 chapters left
We are currently at chapter 1054
1054 + 108 = 1162
Adds up pretty close to 1200.