The idea makes some sense, but I think it would make registration quite difficult for some of the legitimate members. It should be noted that a large number of new members do not come from an English-speaking area, and that they would probably not understand the question/s - and would give up registration. It seems to me that this is not just about bots, but a lot of real people who have bad intentions and see in this forum an opportunity to achieve them.
I have to admit I had to look up what exactly it means shadow ban, and it is true what you say that there has been much discussion on the subject in the past. But taking into account the number of newly registered members (a year ago 20 000 new accounts per month based on this thread) some conclusion is that the staff/mods would have about 3000 posts per day to check on this basis alone, and to that should be added all the regular reports.
Yet the idea has potential, perhaps this post gives a better insight into how the whole thing might work.