Now that accepted answers are in the process of being unpinned, and that's likely to happen on meta sites too, we probably need another way to pin certain answers to the top. This will go in line with my other proposal about creating an "index answer".
So, I suggest that on meta sites, moderators (and possibly other staff members) should have the power to pin a certain answer to the top regardless of vote/sort. That answer will need to have some visual indication that it's a pinned answer.
This will have two useful use cases that I can think of:
Pinning index-like answers or answers that provide a summary of all other answers (see the link above for more details)
Pinning official answers that might not be well-received but still have some level of importance because they reflect the company's (or moderators') decision about a certain discussion/request.
This will also be better than keeping accepted answers pinned on meta sites as a workaround because pinning the answer will no longer be in the OP's hand.
Not exactly the best illustration but maybe something similar to this: