Asking devs to build their own dependency system for the changes is also part of the issue. Really the only way I can think of is some sort of DAG of DDL blobs

Asking devs to build their own dependency system for the changes is also part of the issue. Really the only way I can think of is some sort of DAG of DDL blobs, but I have no idea whether you can express a combination of DDL and DML changes into the one tree so that they can be properly diff'ed. Changes in production are not just changes in the schema, there are changes to data as well. Really the entire RDBMS needs to have "time" and DDL incorporated into the relations.