The last two Q&A:
This former editor of Oda said OP got its ending roughly and already finished 60~70% of the whole story. It will end within 10 years.
Thanks , Kaze!!!
–- Update From New Post Merge ---
While you'd think to trust a former editor….I wouldn't trust the former editor. It will probably not end within 10 years. It's too popular and will probably be plagued with "Naruto-war-lasts-way-too-long-because-its-ending-itis". But in this case, it probably wouldn't be too bad with OP. There's still way too much story to tell. I do not see it ending in 10, probably 13-15. Not with all of the character tie ups, etc.
Correct me if i am wrong but i heard that Oda reveals lots of things about the story of One Piece as well as the ending to his editors . So maybe the series won't end like in exact 10 years but it could be close to that .