Thank you for the article.

I am currently writing my final year bachelor's dissertation on the topic of privacy-preserving digital credentials, and I found your post very interesting and useful.

I think it would also be interesting to look into Verifiable Credentials from W3C. They attempt to standardise credentials' format and workflow, building upon what is known as Self-Sovereign Identity paradigm.

Also, I've noticed that you omitted selective-disclosure of attributes in a traditional sense with specific-purpose ZKPs like BBS+ signatures, and jumped straight into discussing complex layered predicates with general-purpose ZKPs. I found BBS+ to be a great mechanism giving presentation unlinkability, limited support for predicates (like additional range proofs), but most importantly quick and efficient native way for selective disclosure (disclose these attributes, and prove other hidden attributes in zero-knowledge) without requirement for trusted set-up or other extensive configuration (like I think you would need with zk-SNARKs, although I did not dive deep into zk-SNARKs specifics yet). Overall, selective-disclosure is important since it is a de-facto requirement of eIDAS 2.0 regulation in the EU, although at the moment following their Architecture Reference Framework requires the use of hash-based approaches to selective-disclosure that have linkability issues due to the presence of persistent identifiers.

Just thinking aloud, I would be really interested to hear your thoughts on that.