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Regexxer is a very cool tool -- a GUI search/replace tool featuring Perl-style regular expressions. It will look at entire folders of files, finding regular expressions and doing replacements, with a coloured graphical interface.
"has a GUI" does not mean "is a desktop application" ;-) Use of the term "regex" (and need to type in regexes) pretty much excludes it from being a desktop feature, it's maybe a power user or admin tool.
At this point, probably not; it's a little too much of a niche utility to be part of the base OS.
It's not just for regexes. It can do regular search/replace in a very friendly way, though maybe it should have a "is a regex" checkbox to avoid confusion when using special characters.