My pet annoyance is also the prohibition of opinion based answers. I've found many great answers, usually the top result on Google. But sadly the question is locked. Sometime the top answer (before the question was locked) was pretty much the right thing to do 5 years ago, but no one can add another answer. I do understand that opinion based questions are a moderation tar pit. But sometimes there aren't that many opt…
Consider https://stackoverflow.com/questions/84556/whats-your-favorit... and the "is another answer going to be useful?" Or https://stackoverflow.com/questions/1711/what-is-the-single-...
The "no opinion based questions" is a clear line that can be drawn (rather than other squiggly lines that are more difficult) that reduces the overall moderation workload.
You'll note that https://mathoverflow.net allows such questions - but they have many fewer questions per day and a much higher percent of the userbase performs moderation actions. This means that you can allow for that additional workload (which is a few questions rather than hundreds or thousands) to be spread across a larger part of the site's users.
If you want Stack Overflow to allow such questions, then get 1% of the user base to close questions that should be closed every day so that the moderation tasks on them don't get too heavy on too small a group of people who would eventually say "we're not carefully moderating this anymore and instead not allowing those questions at all."