In the interest of good SEO, it would be nice to be able to add content or a description for each tag that users create when they ask questions. Since each tag becomes it's own page, being able to add even just 100 words of content for each one that would then show up on the top of the tag page can significantly improve the appearance of the page to Google and can help drive additional traffic without much extra work.
The simplest way I see this working is having a "tags" page in the admin section that has a table with the tag name, content/description, and an edit link.
If this can be done entirely through a plugin, I'd be willing to look into building this myself and contributing it here. I would just need a few pushes in the right direction to get me started.