According to a Japanese game retailer, DQX's packaging contains a registration code, which made the retailer speculate that it would be impossible to resale the game. This isn't confirmation, so stay tuned. [Game Shop 1983]
This isn't that unusual. I remember that Phantasy Star Online had the same thing (at least... it did on the Gamecube/Xbox with Episode I & II. Never set up my own account on Dreamcast.)
I mean, I think it's a bad idea on Square Enix's part, considering a game with a paid subscription guarantees that you're making money on any used sales... but then again, did they ever say it was going to have a paid subscription?