I think there should, or could, be a way to see the history of changes on a field type.
For example, if a “Single Select” field turns into a text field, it can create an opportunity for errors and misspellings to occur. I’m dealing with this right now myself, and I have to go through each option manually now to eliminate duplicates.
I would love to be able to see who changed the field type, so I can explain to them why it needs to be “Single Select”.
I think it would basically be extending the ‘Activity Log’ feature of individual records to the fields themselves.