I'd like to understand this situation a bit better -- which vocabularies would this affect, and why is this enhancement important? We could prioritize our work better once these are clear. :)

The vocabulary in question is Metatietosanasto (https://finto.fi/mts/fi/) for which I am the technical maintainer. Metatietosanasto has its hierarchy based on groups. The problem arises from the fact that users would like to have (some) groups in groups tab to be sorted in a fixed way but this is not possible at the moment due to the issue described above. See, e.g., http://urn.fi/URN:NBN:fi:au:mts:m4979 where a more appropriate ordering would be non-alphabetical "Teos, Ekspressio, Manifestaatio, Kappale, Toimija, Suhteet, Ajanjakso, Paikka" listing in Finnish and likewise in Swedish (i.e., one must have a language-agnostic way to set the ordering of identifiers - hence the skos:notation approach could work).

In case you are wondering on what else to prioritize I would heavily suggest #810 to be tackled ASAP as solving that would allow Metatietosanasto (and propably other vocabularies, too) to prosper big time.