[X] Machine Spirit Quest
I really like both ideas, although consider the site seems to be allowing NSFW content if it's fitting the narrative She Who Thirsts could be ok (you'd probably need to run the most graphic stuff by the staff first, however), but I understand your hesitance and of course it would be your neck on the line, not mine so it's your right to make the call. Plus I don't want to pressure you into writing messed up stuff if you don't want to (although I suspect any Chaos entity can go completely nightmare fuel as any of the others under the right - or rather wrong - interpretation).
But I'm lending more towards Machine Spirit simply because not only does the power progression sound more non-standard I also haven't seen a quest where you primarily act indirectly through others before, which I can understand people may have reluctance over surrendering so much agency but I'm always open to experimenting with new quest mechanics, which can become quite stale even if perfectly adequate - looking at you CK2. Then again these systems tend to be repeated because they work so well (CK2 has a great system for many quests after all), and I tend to focus more on the narrative accept anyway, but still, I'd like to give it a go. Plus it was mentioned that eventually, we can work towards increasing our ability to act directly so it's by no means an absolute.
Nevertheless, I love both pitches and would be very interested in either quest. Excited to see where either (or both) ideas go!