well ESS has such a facility.
However, I think Mathematica has a super scheme: unbalanced brackets
show up
in red, making them obvious.
This is particularly good for spotting wrongly interleaved brackets, as
in
([ blah di blah )]
<note bracket closure is out of order>
in which case both opening braces are highlighted in red: and the
system won't
accept a newline until the closures are all correctly matched.
Would anyone else find such a thing useful?
Could the ESS team make something like this happen?