Add an API that can be used to cancel or modify the editing of files and folders. For example, you can introduce Editing and Edited events for the dialog which can be fired when the selected file goes into edit mode and after the editing is committed.

FileDialogs are constructed by RadWindow and ExplorerControl as its content. 

Explorer control holds navigation tree, autocomplete, filtering combobox, main pane for viewing fodler and files, search box, breadcrumb. You can check all visual parts in the following help article:

http://docs.telerik.com/devtools/wpf/controls/radfiledialogs/visual-structure

Users might need to put the ExplorerControl in non-window parts of their application (for example in docked RadPane of RadDocking. Also, they might need to override OK/Cancel commands for that purpose.

Click on Drive / Folder in the Navigation tree should put its Name in the AutoComplete box and then pressing the Open Button of the dialog should choose the selected drive / folder and close the dialog.

Expose a ShowReadOnly boolean property which will indicate whether the dialog box contains a read-only checkbox and ReadOnlyChecked property indicating whether the read-only check box is selected

Overrideble properties / methods in DialogViewModels could be added to support custom (or filtered) sources of the navigation TreeView and navigation Breadcrumb.

As a temporary solution, users might filter the breadcrumb this way:
 var breadCrumb = (sender as RadOpenFolderDialog).ChildrenOfType<RadBreadcrumb>().LastOrDefault();
            if (breadCrumb != null)
            {
                RadBreadcrumbBarItem bar = breadCrumb.ItemContainerGenerator.ContainerFromIndex(0) as RadBreadcrumbBarItem;

                DirectoryInfoWrapper bDrive = bar.Items.OfType<DirectoryInfoWrapper>().FirstOrDefault(dir => dir.Name.StartsWith("B"));
                bar.Items.Remove(bDrive);

                DirectoryInfoWrapper rDrive = bar.Items.OfType<DirectoryInfoWrapper>().FirstOrDefault(dir => dir.Name.StartsWith("R"));
                bar.Items.Remove(rDrive);
            }

To filter the treeview:

 var tree = (sender as RadOpenFolderDialog).ChildrenOfType<RadTreeView>().LastOrDefault();
            if (tree != null)
            {
                tree.LoadOnDemand += Tree_LoadOnDemand;
            }
   private void Tree_LoadOnDemand(object sender, Telerik.Windows.RadRoutedEventArgs e)
        {
            RadTreeViewItem clickedItem = e.OriginalSource as RadTreeViewItem;
            List<DirectoryInfoWrapper> dirsToRemove = new List<DirectoryInfoWrapper>();
            foreach (DirectoryInfoWrapper dir in clickedItem.Items.OfType<DirectoryInfoWrapper>())
            {
                // removing drives 'R:' and 'B:' for testing purposes.
                if (dir.Name.StartsWith("R") || dir.Name.StartsWith("B"))
                {
                    dirsToRemove.Add(dir);
                }
            }
            dirsToRemove.ForEach(dir => clickedItem.Items.Remove(dir));
        }

Add a mechanism that allows show/hide the context menu that opens when you right click on an empty space in the dialog. For example, you should be able to hide the "New Folder" or "Properties" options.

Create a property that allows to show the UNC name instead of just the drive's letter or change the implementation of the control so this can be achieved by code.

Expose an event that allows you to cancel the navigation to a folder. For example, if you enter an address in the breadcrumb, click the back button, or select a directory in the navigation tree, then you should be able to cancel the navigation.

This can be done via a new event that have a Cancel property in its arguments, for example.

The naming shown here is not mandatory.

Add localization support for RadFileDialogs.