At first the numbers I saw surprised me (~24,000 according to Famitsu)... but, then again, do MegaTen/FE fans really have a reason to own a Wii U? I don't know how the media campaign was handled in Japan and what they marketed the game as, but I can see how this would be a hard sell given how it started out as "SMT x FE" and turned into something that didn't line up with most people's initial expectations.
Still day one for me though. I'm glad they changed that costume, cuz it was the most bizarre looking thing in the trailers. And that's saying something.