Nielsen DMAs are the most commonly used geographic designations in the marketing communications field and should be added to the pre-defined geographic role options in Tableau.
The definition of these geographies is readily available publicly and would be very easy for Tableau to add to the list of 10 pre-defined geographies that already exist.
Some community folks have used the "build your own custom territories" capability of Tableau to define DMAs. However, these solutions are no where near as user friendly as being able to use one of the geographic roles pre-built into the software.
This is an inexpensive quick addition to the software that would result in many very thankful users!