Sideloading apps on Windows 8 Pro - deployment

Question

I'm currently playing around with sideloading of Windows 8 applications in a corporate environment. Our customers will most probably run Windows 8 Pro on x86-based tablets. Deploying an application with the PowerShell works (rather) well, as long as there is a developer account registered on the target device. If it's not, the following error will occur when the app gets started:
This app can't open
There's a problem with ~AppName~. Contact your
system administrator about repairing or reinstalling it.
The root certificate of our CA is installed on the device and the Allow all trusted apps to install group policy setting is properly set. The device is in an (experimental) domain. On Windows 8 Enterprise it actually works like a charm.
Regarding to this article on TechNet, for sideloading on any other Windows versions than Enterprise a "sideloading product activation key" is required. I searched for more information about such a key, but I didn't find anything.
So my question is: what is a "sideloading product activation key", who generates it and how do I activate/enter it? Or does this phrase mean we need to choose Windows 8 Enterprise?

Answer 1

http://blogs.msdn.com/b/windowsstore/archive/2012/04/25/deploying-metro-style-apps-to-businesses.aspx says « [you need to] activate a special product key on the target machine to enable sideloading. We'll go into more detail about how [to] acquire the product keys in an upcoming blog post. The product key only needs to be installed and activated once on the PC».
The latest I found (August 28th): http://social.technet.microsoft.com/Forums/en-US/w8itproinstall/thread/3092a681-b9cc-473b-83aa-b492ea7f3946
... says «An Enterprise SKU is not required (for sideloading on Windows RT or Windows 8). You can side-load on Windows RT or Windows 8 Pro if you've activated a Sideloading Product Key. Details on how to get such a key are not yet available».

Answer 2

According to this article on ZDNet, you need to buy the keys required to enable sideloading on Windows 8 Pro (as long as you don't want to stick with a developer license). If you search for the given SKU (J7S-00005), you'll find some shops selling bundles with 100 keys for 30€ each.

Answer 3

The official documentation for sharing your app is here. The answer comes in two parts:
The script performs the following steps.
...
Step 2: Verifies whether you have a developer license. If the script doesn't find one or your current license has expired, you're prompted to get one.
To get a developer license, you must have a Microsoft account. For more information, see Get a developer license (Metro style apps).
Before the Store accepts your Metro style app, you must package it and get it certified according to certain rules. If the Windows Store hasn’t certified a Metro style app, the app can’t run on Windows unless you have a developer license installed on the local machine or the app was sideloaded onto the machine by your enterprise. (This restriction doesn’t apply to desktop apps.) Sideloading is the process of installing apps that were not distributed through the Windows Store, usually for testing an app before it is ready for sale. For more info on sideloading, see What is sideloading? Does the Windows Store allow it?
Link to get a developer liscense without visual studio.
Getting a developer license at a command prompt
If you aren’t using
Visual Studio 2012, you can get and manage developer licenses at a
command prompt by running these commands in Windows PowerShell:
Show-WindowsDeveloperLicenseRegistration. This command opens a dialog
box from which you can get a developer license and install it on the
local machine. To run this command, you must have a valid Microsoft
account. You also must run this command in a command prompt with
elevated permissions.
Get-WindowsDeveloperLicense. This command
returns an object that has two properties: ExpirationTime and IsValid.
ExpirationTime is a System.DateTime structure that contains the date
and time when the license expires. IsValid is a System.Boolean that
indicates whether the license is valid. You can run this command from
either a non-elevated command prompt or a command prompt with elevated
permissions.
Unregister-WindowsDeveloperLicense. This command warns
you that some Metro style apps will stop working if you remove the
developer license from the local machine. If you choose "Yes" (the
default) to confirm that you want to remove the license, the license
is removed from the local machine. You must run this command in a
command prompt with elevated permissions. The examples show the basic
PowerShell syntax:
C:\PS> Show-WindowsDeveloperLicenseRegistration
C:\PS> Get-WindowsDeveloperLicense
C:\PS> Unregister-WindowsDeveloperLicense
Alternately, as you mentioned, you can side-load your application. Documentation for that is found here. Further information linking to the msdn on side-loading here.
The main point on the required key is:
Currently, the Consumer Preview and Windows Server 8 Beta are
classified as “enterprise sideloading enabled.” This means that when a
PC is domain joined, it can be configured to accept non-Windows Store
apps from their IT admin. Moving forward, this functionality to
install non-Windows Store Metro style apps will be available for
Windows 8 Enterprise Edition and Windows 8 Server editions.