I'm not sure that you are using the term "delegate" in the sense it is normally used in Qt. A delegate in Qt is a helper for a view to extend the display options for data in the view. You don't assign delegates to models or proxies, you attach them to views e.g. QAbstractItemView::setItemDelegate().

You can either derive from QStandardItemModel and override the data() method to provide an inspection point or you can overlay a proxy model that provides a monitorable data() method. I'd probably opt for the first unless you already have a custom proxy model. However, the QStandardItem is just going to regurgitate exactly what you put into it when you created it.