Whale, let's try to sort this one out.
Let's say ZUN wanted to keep the plot continuous like he did with MoF. Now, it's not entirely implausible to suggest that Yumemi's Improbability Device or whatever it was could have been buried underground and brought up by the geyser. However, this begs the question of how it got there in the first place (just saying "improbability" doesn't count).
Then you have to bring in the question of how Luizeiyuri, Shinki, and presumably Yumemi (replacing Ichirin...? Nice demotion) would fit together, as neither of the PoDD duo has any business in Makai and the only two that know of each other are Chiyuri and Yumemi.
Or maybe ZUN didn't want to do strawberry cross danmaku. The world may never know. *shrug*
Well, if ZUN
was trying to bring back Chiyuri and Yumemi while making sense, he wouldn't include Makai at all. You know, the UFO that we have right now is because ZUN wanted to use new characters. I'm sure he can change the story around
if he wanted to use different characters than Captain, Syou, and Byakuren in the first place.