I would assume that data loss for a migration to 4.1. is not an issue, as the searches, visualizations and dashboards are saved in the Kibana index of elastic search. Including scripted fields I assume. Can anybody help/confirm if I am correct with my assumption? Would like to make sure I don't loose any data.
I had no problem on the upgrade, you could always snapshot the .kibana directory as a backup if your worried. Probably a good practice incase someone deletes a dashboard or other issues.
A massive +1 to this, it's a great idea to be doing!