Microsoft has pushed out Windows RT 8.1 Update 3 that brings the Start menu to the OS. Seeing as Microsoft has not publicly announced this release, we are still working to determine the exact update but it looks like it is KB3033055 that enables the feature.
As you can see from the image in this post, the Start menu looks similar to that of Windows 10 with the inclusion of tiles but the left side of the menu looks closer to that of Windows 7.
Microsoft said that they would bring a Start menu to the OS during the month of September and this update delivers on that promise.
For those that are curious, you do have the option to retain the Start Screen if you do not want the menu.