Another problem that you may not have thought of: Several sub-kilo-karma users may realize the same useful and valuable thing to comment (say, a reference link

Another problem that you may not have thought of: Several sub-kilo-karma users may realize the same useful and valuable thing to comment (say, a reference link or clarification). They all post this before the first one gets endorsed. All the others get penalized with a 24 hour no-posting timeout, for contributing a thoughtful/useful post. (maybe a few of them will eventually get endorsed, so they may suffer a somewhat shorter penalty, at the cost of everybody else seeing duplicate content)