Yup, this is Windows Continuum.
https://support.microsoft.com/en-us/help/17280/windows-10-mobile-continuum
It's neat, though I'm still bitter that Microsoft dropped Windows RT and their respective Surface RT devices when they could have just implemented this mobile OS there. Not going to buy more betas Microsoft.

And I already mentioned it in another thread this Friday. Google is also going this way with Andromeda.
http://www.techradar.com/news/software/operating-systems/google-andromeda-everything-you-need-to-know-1329834

User Requested removal

That 6''-phone is almost as big as my Windows-tablet... and that tablet has a full Windows 10 version, not a dumbed down Windows Phone version. It was also a lot cheaper (even together with the costs for my Android phone) and has a full MS Office version as a bonus.

If you don't absolutely need to have all functions in one device, two separate devices are often better than one hybrid which is jack of all trades, master of none.

Yeah i can see the NX being very similar to this.

TBH i could see this being mainstream 10 years from now when the technology is more polished and powerful.   

This is what Ubuntu phone was supposed to be, but once again M$ beats them to the punch.