As taken from here:
1UP: A lot of fans are still asking for a proper sequel to Chrono Trigger, which was a game you worked on. Would you ever want to work on a sequel? Or would you ever want to see a sequel?
YH: Since everything I would like to do can be done in a Dragon Quest title, the chances of me making a sequel to Chrono Trigger are unlikely. Although as long as the title is interesting I'd definitely love to check it out and play it, even if it's not Chrono Trigger.