It's really difficult to say without knowing how many they shipped. I mean, people that live in a small town in Japan were saying in another thread that they'll be able to easily buy it without having the system preordered and you can still buy it on amazon.co.jp now. That tells me that either sony is supplying a rather large shipment (700-800K+) or demand is not that high. I do not want to guess because I simply do not know what the shipment number is. I'll say that 300-350K would be in line with PSV, WiiU, and 3DS though. What I hope Sony does is get DQ and MH on PS4 soonish. Rumor has it no mainline MH outside of Nintendo systems until after this Fall, but if they make a deal with SE and announce a port of DQX and an HD port of DQVIIR (even if only on PSN) with the promise of DQVIIIR next year, the outlook post launch for PS4 would look better and healthier as other companies with jump on it too.
Also, where are the pics of people lining up in Japan? That's half the fun of seeing a system launch over there.