Dragon Quest X was first revealed in December 2008—almost three years ago. If a former Square Enix employee is to be believed, the company has been working on it much longer than that.
According to former Square Enix developer Takehiko Hoashi, the company's been working on DQX for the past six years. If the title is released next year, that means it's taken seven years to release the title. Then, there's the Wii U version that still needs a release window.
Hoashi is an industry vet, developing games since the early 1990s at Banpresto. He left Square Enix last year, after most recently working on titles like Final Fantasy XIV and The 3rd Birthday.
His original tweet has since been deleted, and his Twitter account is protected. The tweet is visible in the via link below.