It will still be big for a Vita game, but don't expect it to hit a million in Japan anytime soon.
It's still 2 weeks away so it's at a low point in preorders, when the preorder first opened it was sitting in the top 10 on Amazon JP for a while. Now it's at #23. It's actually above DQX for Wii U now, which only a few days ago started in the top 10 on Amazon as well...
The next big game release day is the 28th, which also coincides with the Vita price drop. The new Ice Silver model preorder is already sold out on Amazon JP, too!
Expect preorders to rise a decent amount in the last week, as a lot of people just wait for the last minute if they don't want the special editions. They might not even preorder at all, although then they risk a repeat of Demon Gaze and people not able to find available copies.
Finally, according to this http://www.joystiq.com/2013/02/21/yoshida-ps-vita-digital-purchases-beat-ps3-each-month/ boxed copies of Vita games are a poor indication of real sales. With Demon Gaze as an example again, according to Experience digital sales were accounting for nearly 50% of copies sold.
Edit: Here's the current ranking for reference http://www.amazon.co.jp/gp/bestsellers/videogames/
