Actually, it makes sense. Let's just look at our own world. Everyone has his own hobbies, professions and friend circles he operates in. You could argue that everyone outside of these boundaries is at first glance just "more humans". At the same time, everyone is his own personality and behaves as such, has certain physical features and state of minds.
It makes sense to flesh even random characters out, it makes the world more lively. Worlds where there are just the "main characters" and "plot characters" and everyone else is villager X / Youkai Y / Trespasser Z are not very immersive because of the lack of existing "personalities".
Alright, I've been working really hard to try and figure out how to explain this, so lets see how I did. First of all, lets suppose that your right and everyone in the real world has a deep personality, and Gensokyo is similar to the real world in this manner. That would be a statement about how much information a population contains; however, that's not our problem. Our problem is about how best to convey the information about that population in a story.
I'm not saying it doesn't make sense for Mystia to have a back story, and unique traits. That is part of making a 3 dimensional character and 3 dimensional characters are good. However, when Mystia was introduced she was playing an important roll for the universe. She was a run-of-the-mill character, showing that not everyone in Gensokyo is special, and establishing a norm for the world. More specifically she was serving this same purpose for Night Sparrows who are supposed to be common (I think). However, when Mystia was given the food cart business and the punk rock bit, she became a unique character and stopped becoming a representative of the norm in Gensokyo, and the Night Sparrows. Again, this isn't a problem for Mystia. Instead it's a problem for the world ZUN is trying to establish because it has lost a mechanism which was establishing the setting for use readers, and that is bad story telling.
What I think ZUN should be doing, if he wants to characterize people in this universe, he needs to make sure to maintain a base of unimportant, "normal" characters so that Genskyo remains a feasible place to exist, and I mean unimportant in all cases, not just unimportant in how Mystia is unimportant in the context of Imperishable Night.
Yeah, I think we can pretty much count on that. Reimu is Shinto, and seems to react to other faiths - even Buddhism - with grudging tolerance at best.
While I agree she will represent Shinto, due to her title, I don't think she'll do it because she wants to. I get the impression that she hates all the religions, even her own. All she wants to do is keep the peace and then enjoy that peace.
Pretty sure the silhouette girl will be the only new character on the game... since creating sprites/frames for a lot of different characters would be too time consuming. But that's still good anyway, at least better than nothing.
That chain of logic doesn't work. Sprites/frames have to be created for a lot of characters be they new or old.
Also, with all this talk about who can and can't be in this game, are we just excluding the possibility that characters can be taken out of the background, and just because they appear in the backgrounds doesn't mean they can't be playable characters.