Leaving aside the modest achievements of the code so far, the missing prerequisite to "automatically" formatting SQL is... just formatting SQL.

Because SQL (broadly) was designed to be "human" readable in the first place, it's grammatically very inconsistent and with a lot of keywords. Much more than other languages in use today such as C.

I've yet to find a pattern of indentation, brackets etc. that satisfies my OCD.

Coming up with an example of a nicely formatted SQL statement is not difficult, but turning that into consistent 'rules' and immediately you find counterexamples using other parts of SQL.