Recently I did a Windows 10 upgrade with ConfigMgr 2012 R2. I used the new Windows 10 upgrade task sequence in ConfigMgr Technical Preview 3 before, but this one was new for me. Looking at Microsoft Technet there is a task sequence and multiple scripts available to do the job. With these components you can start an in-place Windows 10 upgrade right away, without the need to wait several weeks (or months) before ConfigMgr vNext is released.
On Microsoft TechNet the following posts are found:
How to upgrade to Windows 10 using the task sequence in System Center 2012 R2 Configuration Manager
Revised content for the Windows 10 in-place upgrade via task sequence for Configuration Manager
Within these posts the upgrade path can be found with the files (task sequence and scripts) needed.
Just create a deployment on the task sequence, and choose Install. In this case I choose an available deployment, so users can start the deployment when needed.
Before Windows 10 installation a Presetup takes place. This runs a corresponding Windows PowerShell script (PreSetup.ps1) to perform a variety of necessary actions prior to running Windows Setup.
This is where setup is actually run from the media package to automatically upgrade Windows. Both Windows media and scripts will be downloaded in the _SMSTaskSequence folder.
Windows restarts into a low-level mode to perform the upgrade and there are two possible outcomes: Upgrade completes successfully or Upgrade encounters a problem and rolls back the system to the down-level operating system.
In my case the Upgrade completes successfully. It was done in around 50 minutes. Additional steps can be added to this group as needed, such as Install Applications or Run PowerShell Script. The Install Software Updates step is provided as an example. The Cleanup step just removes the local staging directory.
Just great to have this functionality in ConfigMgr 2012 R2 too!