It sounds like you've already got a direction here, so I'll chime in with some more general advice. All the time my savvyheads, my hocusses, they throw shit at me. My current hocus is all about building webs of connections in the maelstrom, and last session she decided that what she really wanted to do, long term, was build a web all the way around the maelstrom and ensnare it.
And in all these cases, where the players say something outrageous and out of left field that makes your jaw drop, a really good first thing to do as MC is to ask "How? What would you do in order to make that happen?"
Because then you can make the savvyhead do the work, right? You can make him come up with the idea that he'll need a weather scrubber. You can make him come up with the idea that he'll need a containment device for the horrible black silt that he's filtering out of the rain. You can make him come up with the idea that he'll need the witches brain in a vacuum jar in order to open the maelstrom up.
When the players announce great big grandiose projects, I always get them to break it down into little steps. It's easier to see how you, as MC, fuck with the little steps, make them hard and complicated, how they interact with your threats and fronts.