Updating Windows RT 8.1, to be held in September will not allow the terminals running this OS, like tablets Surface RT and Surface 2, support universal applications developed for Windows 10.
A “Windows base” excluding sub RT terminals
The concept of universal applications is an important change introduced by Windows 10. These applications are able to detect the form factor of the machine, thus adapting to all screens, and work for all Windows 10 machines, through a “Windows base” common to different terminals. For this reason, Microsoft continues to encourage developers to embark on the design of universal apps.
Universal applications are still few compared to those available in RT, but with the ever increasing doubt using Windows 10, they should gradually invade the Windows Store unified.