I am the author of the XACML wikipedia page and I work for one of the leading vendors, Axiomatics.
Yes, XACML is very much used across a wide range of verticals: from finance (a lot of banks even implemented their own engines as early as 12 years ago) to defense (a lot of export control-related use cases) and healthcare (after all you need to prevent your company from ending up on HHS's Hall of Shame.
In the last couple years, we've seen 2 new vendors and 2 new open source implementations surface (AuthZForce for instance is part of an EU project and is backed by Thales, one of the leading Defense companies globally). We've also seen the birth of ALFA, the Abbreviated Language for Authorization, a lightweight notation for XACML and the definition of a JSON/REST Authorization API based on XACML (I actually wrote that piece myself). Axiomatics has expanded the use of XACML to Big Data and Cloud.
It seems to me that most companies do not care so much about personal
data protection (mostly because of the profit and insight gained from
data analytics and ads), so I doubt that personal data protection is
thoroughly employed.
There are severe consequences for not implementing privacy rules. GDPR is one such example. This is the penalty:
If it is determined that non-compliance was related to technical
measures such as impact assessments, breach notifications and
certifications, then the fine may be up to an amount that is the
GREATER of €10 million or 2% of global annual turnover (revenue) from
the prior year.
That's a huge number. You definitely have an incentive to comply. And that does not include brand damage of course. Take a look at Equifax. Who trusts them nowadays?
And in the US, HIPAA is a piece of legislation you need to keep in sync with.
Remember that privacy is not the only reason you would want to use XACML for. XACML is a policy-based language. It is aimed at authorization i.e. determining whether a user can or cannot do a given action. It does not have to be about data privacy. It could be about business processes or trade secrets or IP protection. For instance, one of the customers at Axiomatics, a leading shoe manufacturer, uses Axiomatics Policy Server to make sure brand secrets are only shared with those managers with the right portfolio.
Ewan's point is excellent too: XACML is only one piece in your security arsenal. It is about deciding and enforcing. But before and after that, you want to do governance, access reviews, identity & entitlement management. You will need to implement the protection of your data at rest through data management & encryption. There is more to security than just the access control piece.
I hope this helps,
David.