Remakes of 4,5, and 6 are basically a given. It's just a matter of when.
I can see 8 happening too eventually seeing as how it's basically the "Final Fantasy 7" of Dragon Quest (first fully 3D title, first game for many western fans).

The real question is if they'll ever do 9. The pain-point there is probably the metric shit-ton of 3D models they'd have to produce to account for all the weapons and armor.
I would genuinely love to see a HD remake of 9 that you could like, play all the way through in online co-op or some shit. That would be amazing.