The next Dragon Quest is in development at Square Enix, according to series creator Yuji Horii.
Horii mentioned the new game at Niconico Super Conference 3, according to a Japanese report translated by Gematsu.
No details were given; the developer said only that Square Enix is “making the next” Dragon Quest.
Apparently other members of the Dragon Quest team were taken aback by Horii’s comment, so don’t expect an announcement too soon.
The last series entry, Dragon Quest 10, is an MMO which has not been announced for outside Japan.