The Data Migration Tool existed before this PR:
The keywords are “migration” or “data migration” or “data migration tool” which you can use like this in a local clone of the frappe app’s repository:
$ git log |grep -i migration
There was a major PR #4144 long before the one cited above, but work on it was done before.
So it had quite a history and an experience.
The PR #17134 also refers to a “hub” in PR #28117, but I’m not sure what this was and how it was linked to the Data Migration Tool.
Anyway, I’m sure that Data Migration as such is needed all the time in many (or even all?) implementations.
Gone, but now what?