I don't really think there needs to be much of a connection between what the Maelstrom actually is and what it looks/feels like for each character to Open their Brain to it. I am struggling to imagine a definition for the former that would preclude anything in the latter.
In the last game I MCed I decided that the Maelstrom had two layers, both of which were the result of some sort of psychic virus. The bottom layer was something like an adaptible, google-enhanced, viral version of Wikipedia -- an experiment to distribute all of human knowledge genetically to all humans. This part of the Maelstrom wanted to help everyone, tell them what they wanted to know, assist them in whatever plan they had, etc. It was present in all human beings born since a little bit before the apocalypse, and included all pre-apocalyptic human knowledge. The players didn't see much of this Maelstrom to begin with.
Instead they mostly interacted with the second layer of the Maelstrom, which I called 'the Static' and which also manifested physically in the world in the form of contaminated snow and water. (It was a Front with a variety of threats.) The Static was a virus released as a countermeasure after the first Maelstrom somehow resulted in the Apocalypse, and it was designed to stop people from accessing the other layer. It was genetically engineered information interference, and it was proactive -- it didn't just stop people from learning more stuff, it actively attacked and stole things that they already knew. The content of this first-layer Maelstrom consisted of all the knowledge it had stolen from people since coming into existence. The information was largely incoherent, since there was no organizing principle. The Maelstrom's personality was aggressive and nihilistic.
So this is clearly a pretty 'defined' take on the Maelstrom, though to be fair the second layer was not developped immediately, but emerged later as part of an answer to the question of what I would do once somebody rolled a 12+ on Open Your Brain, and also because one of the characters was actively engaged in +augury, which I decided could access both layers equally effectively. But even though it's pretty defined, both in terms of personality and in terms of what sort of information is available (and what perspective it might have on that information), it is largely agnostic as to what it might feel like for any particular PC to access it.
For example, if I remember correctly, we had the following 'what it's like' answers for our PCs:
For The Maestro D', the psychic maelstrom was a garden that represented his establishment, which manifested information with sort of symbolic plant-life and flora/fauna interaction -- weather also played a part, and simple dreamlike intuitions.
For our Savvyhead, the psychic maelstrom was a radio station, or a series of radio frequencies, broadcasting bizarre messages. (This was the original inspiration for The Static and all the related Maelstrom and Weather fronts, etc.) Sometimes information would simply be spoken over one of these frequencies, but more commonly it would be intuited through a sort of passive, trance-like receptivity to the patterns beneath the static, or a combination of all sorts of different stations blending together.
Our Battlebabe entered a sort of fugue state of extreme focus/relaxation (a parallel was drawn with ultra-high-performance athletes when they are fully engaged in an activity) in which he saw first-person visions, either of the future or the past or other people.
So while I would think about my Static-y maelstrom when considering what sort of information was available that was relevant to their questions, and what sort of attitude/agenda might colour that information, it would usually pass through a final layer of translation before it got to the PC. And in some cases that meant they actually got pretty different information, or levels of information. The battlebabe generally got the most coherent information, but it was usually limited to factual visions; the Maestro D' tended to get really allegorical versions of things, but they hinted more explicitly at a much larger picture; and the Savvyhead kind of vascillated in between those two extremes, depending on what was being asked about.