Introduction
ISO 15926-2 is 21 years old, and needs some updating.
This is how this exercise fares.
A sad story
One solid year ago I made some proposals to update Part 2, in line with the topic  Extended Data Model.
A small team was formed with folks that are busy implementing ISO 15926 in some form. Their complaint was, and is, that Part 2 is so difficult to implement. But they overlooked that Part 2 is a conceptual data model, and the function of such a model isn't a direct basis for implementation. See the topic The three-level architecture of ISO 15926.
Unfortunately each of these implementers tries to pull Part 2 in their direction, so that their implementation becomes compliant. A typical case of the tail swinging the dog.
This may destroy the integrity of Part 2. Only the member nations can prevent that from happening.
