If you look around Mathematics Meta, there are many feature-requests which are marked neither status-completed nor status-declined. In many cases they are probably waiting for further input - for example, if the post has score 2 then it is far from convincing that the feature is needed. But there are also quite a few highly upvoted feature requests where no action has been taken.
If I remember correctly, it was mentioned a few times on meta that Stack Exchange staff monitors local metas for feature requests and bugs. So one thing to do is just wait patiently and hope that eventually the post will be noticed by somebody who can do something about this. Is there something else I can do if I see feature request which I consider useful to help it at least be looked at by Stack Exchange staff?
A few additional questions which seem natural:
- Are per-site-metas really checked for feature requests? Is there a realistic chance that a feature request suggested here get implemented? (This question is relevant if it is a feature that influences the whole network and not only this site.)
- Does a feature request has better chances if posted on Meta Stack Exchange rather than on local meta? If I see here a post which was well received, should I urge the OP to repost there or, if they do not want to, do it myself? (Of course, there are feature requests which are site-specific, in those cases this is not an option.)
- How much does this depend on the score? Does it help if I promote the feature question among other users (for example, in chat or in comments - if there is another related discussion where this feature request is relevant) and get more feedback and possible a few more upvotes?
- Do moderators have some better channels than regular users to bring feature requests to the attention of Stack Exchange team?