There is NO WAY that BW had more sales that XY will. No. Way.
I think XY is going to break records tbh. No matter how much people might complain about the lack of pokemon an blah, blah, blah, at the end of the day, they are still going to buy the games.
The 3DS install base is only a fraction of what the DS install base was at the time of BW's release.