Should there not be a task closed date?

Would be nice to know when a task has been closed, so you can compare it with the due date.

It’s easy enough just to add the field and then either a workflow or on-save hook to populated it when the status changes to complete.

I agree, I think mysql/mariadb they are also called triggers. Maybe I can add it to 7.12.7, depends a bit on release management, maybe changes to db go in into 7.13

Simply turn on the auditing for that field and you have a timestamp for each status change.
I would not recommend using database triggers, rather use hooks or workflows to keep the business logic in one place.

And make it even more slow?

If you think that is causing more issues than mysql-triggers, feel free to do that, it was just a friendly suggestion.

Say if I would do this, how would this go with pull requests and versioning? For now the 8 version does not even work with a default install, and it seems to be still slower than 7. So I do not mind contributing such thing to 7, if I would apply this myself.
I also would like to apply a real duration to calls[1]. But I need to be informed how releases are updated, is there some versioning on the db, where are the db version updates stored in sql files? etc