Funny you should mention it, I thought about this yesterday (not for the first time), and was planning to collect a list of challenges for the retagging today. I'm definitely in favour of this, because these challenges are fairly hard to search for, because the terminology in use may vary a lot ("parenthesis", "bracket", "brace", "matching", "matched", "balanced", "parenthesise", ... are some of the words used to describe these tasks).
However, I'd suggest the tag name balanced-string to make it a bit more general. If someone makes a challenge where
y take the role of
) it's still the same even though no "brackets" are involved (and there is at least one challenge about balanced binary representations).
I'm happy to do the retagging myself over the course of several days, so that we don't bump everything to the front page at once.
As an aside, I would probably also put this tag on challenges related to balanced strings, like Catalan Numbers (I don't know if we have many others that fall into this category).
I've tried as best I can to find all the relevant challenges. I've turned up 32 of them (which, I believe, makes this my biggest new-tag project to date)
and will start with the retagging tomorrow and have added the tag to all of them (see the revision history of this post for the full list). I've also set up tag synonyms with parentheses, brackets and braces so that they show up in the auto-completion, and filled in the tag wiki as well as amended a few related ones (particularly palindrome and syntax).