Dear Erik,
It is already possible to export and import Wikibase items via the main
export and importing mechanism provided by MediaWiki. This process retains
the IDs. I have created a little guide at
https://wikibase.consulting/transferring-wikibase-data-between-wikis/. I
did not address creation of new items/properties after such an import yet,
so beware that an extra step might be needed.
I agree with you that it is useful to retain IDs. My company is helping the
German National Library with importing their GND dataset into Wikibase. ID
stability is important in this project. What's more, since the GND already
has IDs, ideally these would be used, rather than new Q-IDs. IDs in
different formats are not supported by Wikibase yet, but hopefully it is
not too difficult to implement, as it seems rather useful for many
projects. I'll be looking into this soon.
Best
--
Jeroen De Dauw | Technical Director Professional.Wiki
<https://www.Professional.Wiki>
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