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InfluxDB
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I think this probably covers it the best.
In terms of the semantic web, trying to semantically interpret the URN (as OP suggests) also seem like a conceptual mismatch, as there are other mechanisms that allow for the same thing in a more "robust" way.
E.g. in RDF one could pack all the semantics into the datatype of a literal like `Norwegian account number "12345678902"` -> "12345678902"^^<http://example.com/accountNumber/NO> (where the IRI `http://example.com/accountNumber/NO` then serves as an identifier for a concept that can be enriched with more information).
> Often http is used instead, where the domain name serves the role of the namespace, because usually a suitable domain name is already registered. Of course, this latter practice has the drawback that one has to infer from context that it is a name and not an HTTP web resource.
At least in RDF-world (which admittedly isn't the only domain for URNs), this by now doesn't have to be inferred, but has over time formed into an undeniable reality.
In RDF from the beginning IRIs have been relegated to identifiers ("It only treats IRIs as globally unique identifiers" - RDF specification[0]) though it has been mixed with a lot of weak language/suggestions to also use IRIs as locators. And a lot of people/institutions did attempt to make follow that suggestion. However, since it's a lot harder to host a system in continuity that delivers content based on an URL (as evidenced by all the link-rot in the semantic web space) than it is to just coin IRIs, using IRIs as locators so rarely worked in practice that nowadays nobody even tries to do that anymore.
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DISCLOSURE: Self-promotion
Born out of the frustration of this issue (and some other issues, such as uncontrolled mutability when using IRIs as locators for semantics), we have built a package manager for ontologies[1] to serve as a foundation for stable semantic data systems.
In it we replace the fickle "maybe an IRI can be dereferenced to semantics" system of RDF/OWL with a package manager that allows for stable versioning and resolution of all the ontological dependencies of your system, so you end up with a stable set of documents that you can then interpret to get to the underlying semantics of an IRI.
Since there is a default registry[3] that even small projects can publish to, this also greatly reduces the barrier to entry for small projects to participate in building and publishing ontological definitions, as there isn't a burden of setting up and maintaining the hosting of the definitions.
We've been using that system for close to a year now as the underpinning for our platform[2], and it's been great so far. It allows us to offer different semantics to different customers (based on the packages they chose to import), and makes managing even a big set of often-changing semantic dependencies tractable.
[0]: https://www.w3.org/TR/rdf11-concepts/#referents
[1]: https://plow.pm
[2]: https://field33.com
[3]: https://registry.field33.com
> Why are URNs not more popular? […] Why has it not catched on?
1. Usability: a developer must register a URN with IANA which is a huge hurdle compared with minting a URI which only requires control over an email address or domain name. <http://enwp.org/Tag_URI_scheme>
2. Cumulative advantage: everyone knows how to dereference an IRI/URI/URL with the HTTP scheme because the software capable of doing so is deployed million-fold, and dereferencing may also lead to a representation describing the resource which is readable by humans and machines. One can't really do the same with URNs, or at the very least it's much less convenient.
3. Flexibility: if you mint a PURL <http://enwp.org/PURL> with an extremely long lived redirecting service (e.g. <http://w3id.org> or <http://purl.org>), you are able to point the identifier to different resources, this indirection leaves you with options over the time of its existence. URNs have no redirects, they need to be perfect from the start, which is not a reasonable assumption when humans are involved.