For those of you who have been following Build 2015 you might've already seen this, but for the rest of you...
Microsoft announced on Wednesday that they are integrating Continuum into the Windows 10 for Phones platform. Continuum is their engine for resizing applications to the current display whether it is 4 inches or 50 inches. While in itself a neat thing, the part that made my jaw hit the floor was when Joe Belfiore demonstrated a Windows Phone connected to an external monitor, BT keyboard, and BT mouse. Using the familiar mouse/keyboard interface he was interacting with the applications installed on the phone that were scaling up to the 27" (ish) display he was using. While the phone still cannot run Win32 applications, for many people in my organization they don't need anything beyond MS Office, a web browser, and Citrix. If I could get people down from 2-4 devices to just one it would be amazing for them.
At this point we don't know what devices will be needed to run this as they haven't been announced. The only thing that is known for certain is that current phones will not be able to connect to the external display in the way that was demonstrated. Hopefully they will be able to utilize Continuum when they're upgraded and then you can utilise Miracast or something similar.
For more info check out Paul Thurrott's article here: https://www.thurrott.com/mobile/windows-phone/3238/here-comes-continuum-for-phones