Item Two: False assumption. Newbies aren't in fact obliged to read the entire sequences before commenting. They can comment about things like their personal experiences, their areas of instrumental expertise, and matters of opinion. They can request citations for statistics, correct many types of factual errors, issue praise, introduce themselves, make jokes, and talk about locally popular fiction and fanfiction. Any of these types of comments can be valuable, can garner upvotes, and does not need to be suppressed.

The type of newbie comment that is problematic is uncommon compared to the unproblematic newbie comment types. When problematic newbies say annoying things that really would be solved by their reading the sequences, they come in one of two types: one, they only needed a link to the correct sequence, and will promptly stop making problematic comments when so linked. These are fairly uncommon; LW has a lot of obvious conceptual house rules, and most newbies seem to stay out of the deep stuff on their own. The second type is a borderline troll or worse, and while such trolls might be kept out of part of the community by the puzzle you describe if you could control solution leak, downvoting and (in a pinch) banning also do the trick without filtering out commenters who, like me, have no interest in solving silly puzzles you make up.

Item three suffers a similar assumption.

Four: Assumes that people make the same inferential steps from concept to concept. I think this is false. Also assumes that people interested enough in LW to try to comment are the "general population"; I think this is also false.

Five: Of course the idea is neat. But that doesn't mean it is a prudent idea, or that it should be imposed on everyone. As a quick-and-dirty test, I would have abandoned the site on Stumblingupon it if this sort of system was in place (and solutions weren't leaked). Assuming for the sake of argument that I'm a valuable commenter, we should tread carefully when considering the introduction of filters that would have driven me away.

Six and seven suffer similar problems.