Hi Sebastian,
As far as why the version notes feature was dropped in Dataverse 4.0, I think some people found it annoying, an extra hurdle that doesn't always provide value. To be honest, I can't remember if the note was required or if it could be left blank. My gut says it was required because I seem to remember being annoyed by it in dev. :)
There's an old 4.0 design doc* that refers to "the burdensome process of creating a whole new version" with a comment that says, "I don't know. It seems like a relatively lightweight process to me. Unless they don't like filling out the text box. Could the notes field be autopopulated with a text-based list of the results of the "diff" (a la question 3)?"
Suffice it to say that if we do reintroduce version notes they should probably be configurable so that people who are annoyed by them don't have to use them. That said, your use case makes sense so thanks again for creating that issue.
Thanks,
Phli