Earlier quoted context omitted.
If AIs were taking over left and right we'd still expect to see some kind of evidence of their existence. Since they'd only be replacing biological civilizations I don't think it would count as the Great Filter, not in the context of Fermi's Paradox at least, as you'd end up with roughly the same number of technologically capable civilizations after the filter.
We can't comprehend intelligence million times beyond us, so speculating about their intention is very wild. Who knows, maybe an universal law of super-intelligence is to keep a low profile.
If you're going to propose a crazy but interesting possibility, you cannot pull the 'can't speculate, they're to superior' card. You already speculate by sharing the idea!