I'm wondering if nulls have been around for a lot longer than we think.
In TS Rushton tells Elspeth about Selmar, what she was like before she was damaged by Alexi and Vega's work (we assume). It sounded somewhat similar to the way Domick changes.
I think Selmar (and later, Cameo) must have had some success in predicting the future, after their minds had been altered/damaged. Once they had been, they didn't live long - and we're told in TSK that Ariel's mulls have short lives.
Then it reminds me of Stephen Seraphim and how everyone assumes he's defective. We find out that he had his memories altered and he's living with Enoch, but that if he's at Obernewtyn he can't help but remember. I wouldn't put it past Alexi (or whoever was in control of the work they were doing) to have tried getting the info out of him first, about the whereabouts of Marisa's map. Only they were careful to not go full null with him, because they needed him alive because of his inheritance.
This partial success gave Ariel the idea that he could do this to anyone with talent, change the nature of their skills and force them close enough to the mind stream that they saw pockets of the future. I'm not sure why he'd bother when he seems to be able to traverse the dream trails himself, other than perhaps it's just him, again, refusing to do the dangerous dirty work.
I'm actually not sure what point I'm making beyond wondering this and finding it interesting.
Good point about Selmar and Cameo being precursors for nulls.
With Stephen, wouldn't Louis Larkin know about it, cause he's been there forever, so would have seen a change in him like he did Cameo. Interesting idea though. Would be nice to have more back story on Stephen, as well as Marisa, I want to know how she found all that information!
All I can think re Marisa is that she was shown it by Agyllians, in one of those dreams that forces characters to act...
With Stephen, he was reclusive and it's possible he was kept separate from the other misfits by Marisa. Or he wasn't altered at all and really was defective. Either way, he could have conceivably been kept out of sight for most of his life.
I always kinda got the impression that Marisa found the knowledge on her own accord (e.g. like a Teknoguilder's thirst for knowledge, perhaps there was even some allure of power) but, when she found out the truth, she wanted them destroyed, and perhaps it was at that point the Agyllian's intervened, having her carve the doors so that the key would be present for The Seeker to access (but too hard H'ryka* to find)
*note deliberate use of H'ryka, not Destroyer :P
Interesting thought on the nulls Min! Lud Ariel is one sadistic character.
I learnt a new phrase today: Intentional Suspension of Disbelief - we were talking about it in terms of Umbridge vs Voldemort; how yes Voldemort is evil but you tend to resonate with Umbridge because she's someone you've come across in your life. I feel like Ariel vs Malik is that similar relationship... just as aside note haha