I'll post some random observations and theories I have after staring at the screenshots for the new game. A lot of these I noticed two days ago, but I didn't get around to posting anything. I don't expect them all to be right, but who knows?
From the logo, it's clear that spring is pink, summer is green, autumn is orange, and winter is blue. What else happens to use these colors? Lives, bombs, power, and PIV, respectively, which are positioned in the same order on the right side of the screen (similar to the last few games). I suspect this is not a coincidence, but we'll have to wait and see if there's actually some correspondence in the game system or if it's a purely aesthetic decision. He might just be using these colors because they look nice.
The symbols in the bottom left corner also have colors. Reimu's looks pink to me and Marisa's looks blue, which is in line with how most people are associating the characters and seasons. The symbol in the Aya screenshot looks greenish, so she's probably in summer mode. However, Cirno is already associated with summer. The symbols must be changeable in game, or there wouldn't be any point in putting something there. My theory is that using a bomb will advance the mode by one season. So Aya starts in autumn mode because she's associated with autumn, and after 3 bombs she ends up in summer mode.
Looking at the Marisa screenshot, she has three mini options trailing behind her. In the Reimu screenshot, she seems to have three mini crows following her, which I assume are mini Aya options. It's hard to tell because of the dark red background, but If you look closely at the Aya screenshot, I think there's a larger crow option next to Aya's head and a mini crow option a bit above that. Thus, there's some mechanic which allows each character to obtain mini options and these mini options can belong to other characters. No clue how this works though.
Speaking of Aya's option shot, it looks like the vertical space between the bullets gets wider as they go up the screen, so I suspect that they accelerate like Aya's EX attacks in PoFV. I also wonder if Aya has Gradius style options that follow her around. It's hard to tell. Reimu's option shots look like they change direction, so they're probably homing.
From all three gameplay screenshots, it looks like PIV gain is just a little more than three times the graze. I think this means that each graze is now worth 3 PIV, and bullet cancels are now worth relatively little. The Aya screenshot has bullet cancels from 2 bombs but still only has 30 PIV from 8 graze. Meanwhile both Reimu and Marisa presumably got a cancel from a midboss and their PIV gain is still only a little bit more than three times their graze.
On the title screen there's a rather conspicuous petal that's sort of magenta colored rather than light pink. There are petals of a similar color in the Aya screenshot. My guess is that it's some sort of seasonal energy, which charges up the gauge in the bottom left corner. I might be completely wrong about this one though since there's almost no basis for it.
I also have a hunch Lily White will appear. I'd be really amused if she appears to announce spring... and then she appears again later to announce spring a second time, since I assume the plot will be about the four seasons being in flux. I don't really think that will happen, but after Tanned Cirno, anything is possible.
