The following is also a pattern, kind of, but it is interesting if you think about it.
Stage 1 takes place in the Misty Lake, which was shown in EoSD.
Stage 2 takes place in the Human Village, but it was shown in IN, which might not make it a pattern anymore.
Stage 3 takes place in the Bamboo Forest of the Lost, which also takes place in IN too.
PCB takes place in the Hakugyokurou, which is basically another world, so IN has to put another stage to replace it.
Following this pattern, which I doubt is going to happen, but as I said is interesting:
Stage 4 should be a place in MoF since PoFV didn't really feature a whole new area besides Higan. The stage might be on Youkai Mountain.
Stage 5 would take place in the Underworld, which is in SA.
Stage 6 could take place in the Hall of Dreams' Great Mausoleum which is obviously TD.
UFO is skipped because Makai is another world.
But this is just for if I were making the game. I'm pretty sure this won't happen. It's just a coincidence to have all familiar stages.
Cirno might have been placed in to have a Misty Lake midboss, and maybe because Cirno is really popular. I am also creeped out of the second boss. All the species so far have been new too.
The music can be catchy after a while. I really like the stage themes and the boss theme of stage 1. Also, stage 3's stage theme has the main theme of Touhou in it. Which the original Bamboo Forest of the Lost stage theme in IN has too. They also sound alike, so there is a chance the stage 3 theme is just a remix. But now that I think about it, stage 1's theme also sounds like it was the Misty Lake theme in EoSD, but made more upbeat and mysterious.