As far as I can tell,  in version 9 (and 10?) the custom group-by feature combined with the kanban view's ability to move cards between columns breaks almost all limits on user modification of fields. Marking fields read-only in any and all views has no effect, and the custom filter and group-by menus include almost all fields without providing any obvious way to limit the choices. 

A look at the code shows this logic for when a card is dragged to a new column

`data[this.group_by_field] = event.target.id;

        this.dataset.write(record.id, data, {}).done(function () {'

No check is performed to ensure that the field is not readonly. Some fields, notably the last_updated fields, will refuse to drag between columns, but that may be due to their date data type rather than to any readonly setting. 

Have I missed something? Is there some way to limit the choices in the custom filter/group-by menus? Is there a way to tell the kanban view that some fields are readonly, as can be done in the form view? Or is kanban view + custom group-by a disaster for maintaining control of data modification by users?