Not a lot of details about when this feature will make it to the mainstream Windows 10 build, ZD Net speculates it will likely be a 2019 feature. Furthermore, it may be a Windows 10 Enterprise exclusive.
The coming InPrivate Desktop feature may be codenamed "Madrid," based on information from the quest, which also described the feature as "an in-box, speedy VM (virtual machine) that is recycled when you close the app."Sandboxie is an example of a third-party tool that lets you run software in a sandbox mode.
Windows Defender Advanced Threat Protection was codenamed "Seville," another city in Spain. And Windows Defender Application Guard was codenamed "Barcelona."