There is no guarantee of that. While the 3DS is not replaced, it's better for them to release it as soon as possible, and then promote the other versions.
People wanting the console version will always get it, double dip or not, and people wanting DQXI but not having a PS4 won't necessarily buy one when other versions of the game exist, especially if they just have to wait a few weeks. They could also perfectly buy a PS4 + the game, then resell them, thus defeating the strategy you've talked about.
As said before, they will have to push FFXV if they want people to buy a PS4 in Japan for their games, not DQXI.