This time there's a workaround for Windows RT sideloading keys also.
|Developer license successfully renewed|
Use the PowerShell cmdlet "Show-WindowsDeveloperLicenseRegistration" to activate sideloading on Windows. This will enable Windows Intune to install apps without a sideloading key being set up. The limitations are that it requires a manual process on the client to activate sideloading, the license is only for 30 days (but can be renewed by running the cmdlet again), and the Windows team reserve the right to act if they feel the developer license registration is being abused.