Well, this has been brewing for a while - builds of Windows 10 on ARM for the likes of the Lumia 950 XL. But don't get too excited, there are still so many caveats. Such as these builds being designed for the USA product variants, or all backwards compatibility for Windows Phone 8.x applications being lost, or the lack of optimisation for all the (in this case) 950 XL special imaging features, or even lack of optimisation for Windows 10 apps fullstop. But still - if you have a 950 XL that's not being used for anything else, then this is a fascinating tech-experiment, even if a little bit of a one way street and with zero official support along the way.

Here's MSPU's introduction:

The LumiaWOA project now has firmware you can download and install using WPinternals which makes installation as easy as flashing with any other firmware. It does replace the Windows 10 Mobile install, so users need to back up their data of course.

If your Lumia 950 XL is only gathering dust in an old draw, there is likely nothing to lose by trying out the hack. 

And from the official instructions page:

Requirements:

• A Lumia device that is supported by available FFU images
• WPinternals, see https://wpinternals.net
• Windows Device Recovery Tool (for thor2.exe)
• A FFU image downloaded

And from the official downloads page:

The FFU firmwares provided here are for testing purposes only. We can't be responsible for any data loss caused by those firmware images. Those FFU firmwares contain only Windows Desktop (Windows 10 on ARM), they do not contain Windows 10 Mobile, and will never contain it. By flashing them you agree to lose your current Windows 10 Mobile installation and replace it with Windows 10 on ARM. Make backups of your data prior to flashing those FFU images. Please refer to instructions on how to flash those FFU firmwares onto your device.

Amazing work from the development team, but...

I have so many questions at this stage - and I'm not going to sacrifice my personal beloved 950 XL in order to try all this. For example, would all this work on a 950 XL from another region, and what about a vanilla 950? How much else won't work? How easy will it be to get back to Windows 10 Mobile and can WDRT be used for the purpose (I doubt it)?

Finally, how much time will it really take to get to grips with WPInternals, FFU images and so on? I've investigated it all a few times in the last few months and have been put off each and every time. Any brave souls out there?