Add support for shapes, and especially for shapes with textual content. 
In OOXML, shapes are represented by the wps:wsp element, and shapes with textual content by <wps:txbx>, <w:txbxContent>.
Such shape can be added to a Word document using the Insert -> Text -> Text Box -> Draw Text Box, or through a shape's context menu -> Add Text.

Do not confuse these shapes with Text/Rich Text content controls (see https://feedback.telerik.com/Project/184/Feedback/Details/190057 )

When exporting a document containing a Field that has no Separator set the content after this field is omitted.

According to the OOXML Specification, the fldCharType value separate is optional. 

When the data is set as double or float the Numeric formatting of the MergeField is not respected.

When the following merge field:

MERGEFIELD BAL  \# ###,0.00

is populated with 5.70F or 5.70D the result is 5.7 instead of 5.70.

In the document produced by the mail merge, the date time and numeric formatting applied are not respected and the value is in its default format. 

 Table with specified width in inches is not correctly exported when the size is set in inches (this is  done in the imported HTML) 

Workaround: set the table size in the code and remove the style.

Add support for Upper and Lower field switches  More info is available here: Formatting fields with switches

Here are the switches that should be supported:

Add support for all number switches.  More info is available here: Formatting fields with switches

Here are the switches that should be supported:

When exporting to PDF a document containing Table merged into a TableCell an extra empty space below the inner table is added:

When we have Document properties set (no Section properties set) and the \sectd control word is missing the Document properties are not respected.

From the RTF Specification: When we have Section properties set the \sectd resets the values to that specified by the Document properties. But when we don't have Section properties set and the \sectd is missing we should inherit the values specified by the Document properties

Implement nested mail merge and master-detail scenario.