In case you aren't aware of this, what you've made is very similar to the rx.el[1] that's shipped with Emacs since 21.1 (released in 2001).
Many of the comments here are speculating on what this might/could be used for, but could simply look at how it's used in various Emacs modes compared to writing raw regexes in string form.
It's not fully comparable, since a large reason to use rx.el in Emacs is Emacs's nasty regex syntax coupled with having no native quoting construct for regex, making writing anything an exercise in bashing your backslash key.
But it also makes it easier to programmatically generate regexes, which as your Python implementation also shows can lead to much clearer code.