I've seen many software developers who aren't familiar with regular expressions! The functionality definitely comes in handy and I even made my own [simple] VBA wrapper for when I do Microsoft Excel work. I prefer using built-in functions when possible to keep maintenance easier for others but I'm not afraid to use regex when I need quick and accurate results.
I make good use of the above mentioned web site when I test my regular expressions, it's a good site!
It's my understanding that the limiting factor is the database. Regex can't be translated into typical functions (INSTR(), FIND(), MID(), STR(), etc.) so either it's supported at the db level or it's not.
Indeed you are correct that certain database implementations are limited in their support for regular expression matching.
This however doesn't change the fact that a secondary regex processing layer can be implemented in Tableau VizQL (or in some ancillary way nearby) to support regex after the data is already present in the data cache.
There are 2 stages (at least from where I see it). 1 at the database layer, 1 within Tableau itself.
Thanks for adding this perspective to the discussion. It is an important distinction to be able to make.