Going by the traditional heavy focus of the japanese market for DQ, the audience they carter DQs games to, is either having a 3DS already (7 games released on the system so far, mainline ports/remakes and spinoffs) or is on mobile, but thankfully we can rule this out.
And i really think you over-estimate the potential of the western PS4 userbase when it comes to DQ. If there is/was an high demand for DQ in the west outside of the gaming culture in the online-space, then SQEX would have already released the 3DS ports without a hassle.
I don't think that the average joe is interested in the maybe most japanese/traditional JRPG DQ, or there are really many people out there with the "not on consoles, no buy"-mentality ... and that would be sad.
Take the Ni No Kuni sales (last number i remember was 1.4 million worldwide, and with the DS version added to that sum), i think that is a good title to compare the sales, and try to remember that the PS3 had a bigger install-base by the time that game released.
And by your logic, let me give you a similar example: Wii got a DQ spinoff early in the life-time (Iike PS4) but it only got the MMO by the time it was already about to be buried.
Oh and btw. SQEX is in no way repsonsible for guaranteeing (is that the correct grammar?) a consoles success. That's Sony in this case. And i think the PS4 can be successful enough with games like FFXV, 7 Remake (if it comes out this gen), Star Ocean 5, Tales of *insert random word here*, etc.
Any by the time those games are out, the PS4 might be lone and dominant leader of sales worldwide, then we have a different situation for DQ12!