If an existing column exists a new one is made anyways, this can be problematic with multiple migrates and rollbacks and could result in a number of repeated columns. (i.e. If I go to add a column named Blah and one exists it will go right ahead and make Blah1)

One potential fix is to have a clean-up script that removes all site columns that arent attached to any content type.

Pass in a json file with appropriate group names and column types etc so that the make file is even more automated.

This would generate the add and delete code.

If this is something we like the idea of let's discuss potential json layouts for this.