It is not possible to implement a ColumnSet because of ColumnSet.targetTables()

fun ColumnSet.targetTables(): List<Table> should not be an extension function, but instead an open fun of ColumnSet. Having targetTables() as an extension function makes it impossible to implement a custom ColumnSet. We would like to implement our own ColumnSet as a wrapper around an Exposed Table to wrap certain methods such as insert, update and delete and hide some of the base functionality of a Table.