I'm actually starting to question what I meant by "the last two times". I have three games that might apply, but one of them was Dream Askew, and one was AW:Fallen Empires.
Last time I played AW, I did exactly what I describe. It was a group where one of the players had played with me several times before, two were new to AW, and one new to roleplaying in general. I talked a bit about the maelstrom: what it's defined to be, what it can possibly turn out to be, highlighting the high variance both in terms of behaviour (does it only ever allow people to gain information, or does it take over people's actions, manifest physically etc) and possible explanations (can it be explained as a "collective unconscious", a field generated by alien psychic satellites, is it practically magic). I stressed that we need not ever decide on a plausible explanation during the game, and if we do we need not reveal it, but I brought up the point that in different games, the maelstrom varies along that axis of explicability.
I also said that despite what I said about my preferences, I would obviously be a fan of any Brainer or Hocus, and allow them the full results of using the maelstrom to further their agenda; I wouldn't want to cripple them in the interest of grounding the maelstrom.
At least one player was still eyeing the Brainer for a long time, but in the end they chose the Maestro D', Angel, Battlebabe and Savvyhead.
Some of them opened their brains at various times – I don't remember very well now. I did the usual thing of asking what it was like for them, and it sort of coalesced into visions and sounds. I did remind them that different people are allowed to experience the maelstrom differently, that's why I ask every character the first time they do it – but they ended up using pretty similar descriptions. This might have been a consequence of wanting to keep it grounded; I guess it feels more gonzo to claim that it's the same thing but it's perceived completely different for different people.
Now, I did decide after about a session what I wanted the maelstrom to be, and kept it in the background until I had sort of given the players a few chances to provide input that might disrupt it. When they didn't, I started treating it as my prep, in the sense that I say what my prep demands. The idea was one that had been kicking about in my mind for a while, namely on wireless computer-to-brain interfaces. I imagined that in the Golden Age, the technology that today only allows a human with electrodes on their head to controla computer, eventually grew wireless, and then bridged the gap in the other direction, so a computer could induce sensory stimuli in the human brain. When this technology had become ubiquitous (a mind-router in every home), some sort of virus or cyber-attack catalysed the end of the world (details unknown).
The Savvyhead found one of these mind-routers, without knowing what it was, and most of her workspacing ended up centering around that. She took Augury pretty quickly. An old woman showed up, drawn to the signals. She was addicted to the higher level of being she had had as a cyborg, so she felt crippled trapped in her human-baseline senses. Long story short, the town distrusted the mind-machine and rallied in a lynch mob to take it from the Savvyhead and destroy it. This was sort of the "Savvyhead's subplot", while the other three were more involved in the snow scooter raiders threatening the town. After the raiders had been taken care of, we spent the last session wrapping up the mind-machine plot.
The mind-machine had every potential for making the Savvyhead Charles Xavier, and turning the game into X-Men. By discussing our preferences beforehand, we all pulled in the same direction, which was that the maelstrom should be mystical, weird, but on the purely physical plain I guess non-impressive. If the correct reaction to the maelstrom had been "oh my god this changes everything we know about the world, and if I can harness this I will rule the wasteland", well, then the game pretty quickly turns into that. I like the maelstrom, but I don't want the premise of every AW game to be "the world's gone to shit, but there's this maelstrom that has the potential to change everything – who will control it?" That's a cool game, but sometimes I want "the world's gone to shit, you're playing the coolest people around, can you make something that will last?" In the same way that we can have a Chopper with really cool bikes without having the entire game revolve around who gets the bikes, I want the maelstrom to be part of the setting without being the most important resource in the world.
It was an important element to our game and narrative, don't get me wrong. The story of the old woman who wanted her old computer-augmented life back, and the Savvyhead eager to help and curious to understand, was a quite gripping tale, pushing the same buttons for me as e.g. Ghost in the Shell.
I don't know how well my solution generalises. The end result, the exact maelstrom we got, was pretty much the product of my own mind; it was apocalyptica that I dreamed up but waited a few sessions before inflicting on the game.
What actually happens when you do "the talk" beforehand like I did, I think, is that you limit the players' view of their choices. Without it, someone might open their brain, experience it as an alternative dimension, fine. Then next time, they ask "can I bring someone else into that dimension?" The next time, "I open my brain and try to find person X". The next time, "I want to open my brain, and when I'm in the maelstrom, I want to focus my entire being on hurting person X". And so on. And before you know it, superpowers. It can be cool, but what I don't like is that the game sort of naturally gravitates towards it – mostly since it can never move in the other direction; you can never de-power the maelstrom during the game. It's a genie-bottle situation.
As I said, we had a Dream Askew game that was pretty similar, maelstrom-wise. I don't care to recall details, this post is long enough. We also played Fallen Empires, and we had a Mystic (Savvyhead) who talked to spirits. That maelstrom pretty quickly became a spirit phone – "sure, we'll just commune with spirit X!" but it was kept limited to that kind of communication, and more importantly, it was only available to the Mystic. In fact, it was the first time I felt that I really manages to make the Savvyhead cool – since "can I do X with magic" "sure! You just need X, Y and Z" is easier for me to use to encourage doing cool stuff, than the corresponding "can I do X with weird tech". I think I'm just not very good at thinking in terms of weird tech (I might be too grounded). But yeah, non-Mystic characters opening their brains kept it to passively listening to the spirits in their vicinity, sort of.