I totally agree things require special handling and interpretation on both sides anyway.
I do not really see any value in forcing my way into URNs for the sake of it. Yes, I could use OIDs, but the result is not self-documenting in the way my examples above are so it would just make life harder for everyone I feel. (Every Danish person knows what a CRV is)
The main thing that bugs me is just having to invent those strings to refer to registries myself.
And many developers will go with "country" instead of "scheme" which is not always correct.