I don't think Dragon Quest XI will necessarily be instructive given that the 3DS version will likely take up 70% of the sales, but Final Fantasy XV and Kingdom Hearts III will be very interesting to watch for that reason.
It will though. The point isn't "is this the only way to play DQXI's story" but rather "how many people are actually interested in a huge AAA console version of DQXI". Big brand, big production values, highest spec available. The 3DS and PS4 DQXI are two different games.
KH3 won't be interesting to watch at all. It's closer to RE than FF/DQ in terms of franchise power in Japan. It could sell fine (800k) and still not tell us anything about the ceiling.