To be fair, even without his current statements, signs have been pointing to Dragon Quest XI being on the PS4.
First, Yuji Horii has always said that mainline Dragon Quest games will appear on the most popular gaming platform at the time, and this generation that is undeniably the PlayStation 4 even if that isn't what Japan might want. Outside of Dragon Quest X which is an MMO, the mainline Dragon Quest games have all appeared on the most popular platform of their generation... the DS was indeed the most popular platform of its generation like the NES, SNES, PS1, and PS2 were. The PS4's only issue is that it's not selling well in Japan specifically, which is where Dragon Quest does best, but...
Second, Square Enix has stated that they want to revive home console gaming in Japan. This is because handhelds have an uncertain future. 3DS only having 50 million sales is an absolutely huge drop off compared to even the GBA and PSP, and let's not mention how poorly the Vita's doing. It is very possible that, because of mobile, handhelds may not have a future. However, home consoles obviously still have a future even without Japanese support given how well both PS4 and XB1 have sold so far. Unfortunately, if handhelds die off without home console gaming being revived in Japan, then Japan will literally end up with an all-mobile future, which is not to the benefit of anyone who isn't taking the majority of the mobile pie like GungHo and Mixi are. Now given Square Enix's goal of reviving home consoles in Japan, what better way is there for them to do that but a mainline Dragon Quest for consoles? That's Square Enix putting their A-Lister for Japan onto the exact market that Square Enix wants to revive in Japan. And if Square Enix does that, then it will be for the home console that is seeing the majority of Square Enix's Japanese support, which is the PS4.
Third, PS4 already got Dragon Quest spinoffs in Dragon Quest Heroes 1 & 2. Usually when Dragon Quest appears in spinoff form on a platform, that platform will get a mainline Dragon Quest game. Dragon Quest Heroes is Square Enix testing the market to see if there is an audience for Dragon Quest on the PS4, which is also why it is coming to the West.
Now, it is entirely possible that Dragon Quest XI is also on the PS3 and/or the Vita as well as the PS4, but if there is a PS3 or Vita version of Dragon Quest XI, it will be exclusively for the Japanese market, while the PS4 version will be the only version released in the West. However, Horii always wanting the most popular platform of the time for Dragon Quest, Square Enix wanting to revive the Japanese home console market, and the PS4 already getting Dragon Quest spinoffs seem to point towards a release of Dragon Quest XI for the PS4.
First, Yuji Horii has always said that mainline Dragon Quest games will appear on the most popular gaming platform at the time, and this generation that is undeniably the PlayStation 4 even if that isn't what Japan might want. Outside of Dragon Quest X which is an MMO, the mainline Dragon Quest games have all appeared on the most popular platform of their generation... the DS was indeed the most popular platform of its generation like the NES, SNES, PS1, and PS2 were. The PS4's only issue is that it's not selling well in Japan specifically, which is where Dragon Quest does best, but...
Second, Square Enix has stated that they want to revive home console gaming in Japan. This is because handhelds have an uncertain future. 3DS only having 50 million sales is an absolutely huge drop off compared to even the GBA and PSP, and let's not mention how poorly the Vita's doing. It is very possible that, because of mobile, handhelds may not have a future. However, home consoles obviously still have a future even without Japanese support given how well both PS4 and XB1 have sold so far. Unfortunately, if handhelds die off without home console gaming being revived in Japan, then Japan will literally end up with an all-mobile future, which is not to the benefit of anyone who isn't taking the majority of the mobile pie like GungHo and Mixi are. Now given Square Enix's goal of reviving home consoles in Japan, what better way is there for them to do that but a mainline Dragon Quest for consoles? That's Square Enix putting their A-Lister for Japan onto the exact market that Square Enix wants to revive in Japan. And if Square Enix does that, then it will be for the home console that is seeing the majority of Square Enix's Japanese support, which is the PS4.
Third, PS4 already got Dragon Quest spinoffs in Dragon Quest Heroes 1 & 2. Usually when Dragon Quest appears in spinoff form on a platform, that platform will get a mainline Dragon Quest game. Dragon Quest Heroes is Square Enix testing the market to see if there is an audience for Dragon Quest on the PS4, which is also why it is coming to the West.
Now, it is entirely possible that Dragon Quest XI is also on the PS3 and/or the Vita as well as the PS4, but if there is a PS3 or Vita version of Dragon Quest XI, it will be exclusively for the Japanese market, while the PS4 version will be the only version released in the West. However, Horii always wanting the most popular platform of the time for Dragon Quest, Square Enix wanting to revive the Japanese home console market, and the PS4 already getting Dragon Quest spinoffs seem to point towards a release of Dragon Quest XI for the PS4.