Regarding Final, maybe there's been some miscommunication, but I said that there appears to be a new artist. At least to me, it doesn't look like Doi's work for the main characters any more. And then there's whoever's responsible for redesigning Nirasawa's artwork. Whether it's the main artist, Nirasawa himself, or someone else, these monsters are getting a different look.
But I agree it doesn't make much sense to change artists for a spinoff like this, so I'm not sure why they did that if that's the case. Unless Doi's work was also criticized like I assume Nirasawa's was. Or unless the game is very fundamentally different than the previous one.
I'd like to see an all Kaneko SMT game again. But I think they're going for mixed designs because they feel like some more 'contemporary' artists are a better look for the game as it's face outwards, for commercial purposes.
It is Doi. Famitsu confirmed it. (Don't read too much of the translation though. There are already spoilers on the premise I wish I didn't see.) They kinda made it sound like Doi did the demon redesigns too, but Doi is 100% still doing the character art. It was very explicit about that.
So they didn't change artists for this spin off, at least not for the characters. They did mention that they are heavily taking fan feedback into consideration, which is great. That's likely why they redrew those demons. It's already confirmed that conversing with demons is improved, which sucks for me since I liked how unpredictable they were since they're demons, not buddies, but to each his own.
I agree that that's exactly why they're going with Doi. And maybe that's the best decision, financially. I just feel like it makes for a vastly less visually interesting end result. I look at Nocturne, and through research, I'm sure I'd like it less than IV because of how dated the gameplay and storytelling is compared to IV, yet I'm so compelled to play through the game just because of how absolutely beautiful the game looks. Seeing that same style, in HD, with all the improvements SMTIV brought in gameplay, would make my heart melt. I even think that, in HD, that might be enough to sell it on its own merits even more than Doi's style.