The tag system is designed to mark certain questions by interest or topic so that users can quickly identify which questions apply to their skill and interest level. Additionally, the tag system is used to help narrow search results so that users can locate questions that meet certain criteria, based on interest or topic.
Meta-tags are the exact opposite in that they tell users nothing about the actual content of the question. Using meta-tags limits the number of actual descriptive tags that can be applied to a question.
In addition, tagging these questions and relying on those tags leaves the door open for regular users to retag those questions and remove the polls tag on questions they want to save.
Instead of using meta-tags, it makes more sense to flag them for moderator attention and then have them closed, or flag them and delete them.
Flags, in addition to not limiting the number of actual non-meta tags, do remain in the system until either manually dismissed by a diamond moderator or when the question is deleted or closed. This seems like a much more robust and reliable way to manage these questions and keep track of those that need attention, as even 10k+ users cannot dismiss the flag.
Finally, what this does do is puts the questions in the flagging queue, which can be accessed by diamond moderators as well as 10k users. Both groups can use the moderation tools to go through these questions, when they have time, and vote to close, vote to delete, or flag for moderator attention and make the case for not deleting or closing them.
Removing the questions from this queue, without actually closing or deleting, is reserved solely for diamond moderators, so we can trust 10k users to help with this process without worrying about any questions falling through the cracks.
In summary, flags give us the advantage of effective tag usage as well as the advantages of knowing that the collection of flagged questions is safe.