When you look at the popular tags on a site, you are presented with a list ordered by the total number of questions each tag has. This means that new tags will be buried below older tags that have accrued many questions over the lifetime of the site, unless the new tag is exceedingly popular. I'm requesting some additional granularity be added to the tag 'popular' view. If you go look at users' reputation, you can see rep gains over different time frames:
This lets you then see which users are exceptional at gaining reputation, which is a sort of popularity measure for users. For tags, I'd say the analogue is how frequently they're being used. How often they've ever been used is one useful measure, but smaller time frames make for more granular data.
The particular use case that caused my request is I was looking at Gaming.SE, and wanted to easily look at tags for some recently-released games. I ended up using the new tags view, which provides a listing of recently-created tags, but I desire something between 'recent' and 'forever'.
This is a sort of resurrection and expansion of the former 'Recent tags' feature, which looked at two things: Tags on questions that are 1) recently created, and 2) are positively scored. (Tags also need to have >3 uses to make the list.) It was killed off a couple years back.