If you still own a Windows Phone device and are in any way involved with the modding community, you've probably heard of the Windows Phone Internals tool. One of the best things about the tool is that it can disable SecureBoot on all Lumia Windows Phones, the equivalent of unlocking the bootloader on your typical Android smartphone. For other phones, such as the HTC One M8, it used to be the case that you were out of luck. That's no longer the case, and there's now a way to unlock all Windows Phones, including all Qualcomm based devices.
At the moment, the only instructions available to unlock your device are a bit tricky to follow. The exploit has been made possible thanks to a leak of a developermenu.efi. developermenu.efi is a tool that was previously used by Microsoft for testing smartphones and allows you to do a number of things on a device including entering mass storage mode directly on the phone, without a computer. This is only a precursor to modifying the device, and a number of steps are required that include modifying the Windows Phone Internals application from its GitHub repository.
If you want to give it a try, you can check out the source link below for instructions. Keep in mind that your only device storage access will now be via the new developermenu.efi that you installed. It can be easy to brick your phone if you aren't careful. However, this hack allows you to disable SecureBoot on the Alcatel Idol 4S, HP Elite x3, and HTC One M8, opening the door to installing alternative operating systems such as Windows RT. Once you've got everything set up, SecureBoot will be switched off regardless of what the operating system actually says.
Given that Microsoft has shifted their mobile focus towards promoting their various services, there's little chance we'll see any Windows Phone successors. Even though Windows 10 Mobile is now in maintenance mode, that doesn’t mean a group of dedicated and passionate developers can’t keep existing Windows Mobile devices usable for as long as possible. We see the same thing happen on the Android side of things all the time, so we wouldn't be surprised if there's still work being done on these devices a year down the road.