Add "Show Grid Lines" command. The command should visualize all table borders, including the invisible ones.

The desired width of the tables is not set to 100 percent. Instead, the width of each column is set to the fixed value in dxa.

A Block element that can contain a UI element like an InlineUIContainer, similar to WPF's BlockUIContainer would be a nice enhancement to the control. 

Add a way to restrict page breaks in paragraphs or page breaks between paragraphs. In MS Word, these options are named "Keep lines together", "Keep with next" and "Page break before".

When there are several instances of RadRichTextBox in the same page/view, it would be nice if only one instance display any selection. 

In the same scenario, the color of the selection of TextBox, for example, changes. Clearing the selection on LostFocus would have been a solution, however control loses focus to the color pickers, comboboxes, etc. from the SelectionMiniToolBar and RadRichTextBoxRibbonUI.

Currently, ParagraphDefaultSpacingAfter and ParagraphDefaultSpacingBefore are not applied to paragraphs in tables. This should be changed for consistency with the rest of the document.

Splitting table cells is currently not supported and it would be a nice addition to the functionality related to tables. Menu item should be added to the default table context menu.

When TextOptions.TextFormattingMode="Display" is set on RadRichTextBox, incorrect Measuring causes TextBlocks to not visualize correctly.

Currently, the only customization that can be performed is using HyperlinkToolTipFormatString property of RadRichTextBox, which sets the format for all hyperlinks in the document of the control. It would be nice if it were possible to be able to set different tooltips. 

Introduce Navigation Pane as an enhancement to the UI of RadRichTextBox, similar to the one in MS Word (View -> Show -> Navigation pane).

In some text editors (e.g. Visual Studio code editor), pressing the Insert button activates overtype mode, where characters are typed over the current ones (the current character is deleted before the new one is inserted). This is not supported in the modern versions of MS Word.

The spellchecker does not recognize words with non-breaking spaces between them as separate.
A workaround when pasting text into the RadRichTextBox is to subscribe to the CommandExecuting event of the control, get the paste text from the clipboard and replace all non-brekaing spaces with spaces.

private void editor_CommandExecuting(object sender, Telerik.Windows.Documents.RichTextBoxCommands.CommandExecutingEventArgs e)
        {
            if (e.Command is PasteCommand)
            {
                var pasteText = Clipboard.GetDataObject().GetData("HTML Format") as string;
                if (pasteText != null)
                {
                    pasteText=  pasteText.Replace("&nbsp", " ").Replace(' ',' ');
                    var originalDataObject = Clipboard.GetDataObject();
                    DataObject dataObject = new DataObject();
                    foreach (string format in originalDataObject.GetFormats())
                    {
                        dataObject.SetData(format, originalDataObject.GetData(format));
                    }
                    dataObject.SetData("HTML Format", pasteText);
                    Clipboard.SetDataObject(dataObject);
                }               
            }
        }

Support for file formats other than .TDF is required, so that a broader range of dictionaries can be used. Consider adding support for OpenOffice dictionaries.

Support (programmatic and non-programmatic) for Word-like real-time text correction and formatting (similar to AutoCorrect and AutoFormat).

Add possibility to export files in MHTML format.

Add possibility to import files from MHTML format.