Seems like a pretty straight-forward port of a feature already in the Run and Bike apps.
The nature of rowing as a sport means frequent stops, though as many of us train on moving water the GPS still reports a very slow movement. This not only ruins the average speed for a session but as the Speed graph in Garmin Connect must scale the display these VERY low speeds, it makes the graph as a whole unreadable. This problem could also be solved by scaling the Y Axis of the speed graph logarithmically (like Garmin Connect's competitors do) to give more prevalence to the data we're actually interested in. At the minute GC is barely fit for purpose as a platform for consuming and review GPS data from rowing and its a shame as the changes needed to really shine are minor.