Comment by hirsin

Launch from Layout is an installation method that allows you to take loose files (an unpacked appx zip) and tell the OS 'treat this as an installed app'. You can do this with a couple WinRT APIs, Device Portal, or WinAppDeployCmd which comes with the SDK.

I own dev mode for Windows 10, and can confirm that these issues have been always solved and recently received more improvements, although the documentation may be lacking. Windows has always supported third party stores and the ability to pass around an appx.