In the last 2 years, I had 2 or 3 people ask me to make a Windows Phone version of my Android/iPhone app... so far it hasn't seemed worth the effort to me.
Of course I might just be lazy.
It depends on ...
I use .NET (normally my preferred languages are Delphi and Python) to create plugins for big CAD systems. A part of this plugins running event driven in the background on every user change to checking or modifying thousends of objects at once. This can't be done if .NET are really slow.
I was talking about the IDE and it's time to compile a few lines of code. it's instant in any other language while VS needs seconds just for an empty project.
I just convert a B4a-App to WP8.1, it's done already to 90%.
Here the time of compiling to the first launch:
Visual-Studio= 13,82 second
B4A= 21,56 second
The app runs in WP8.1 very nice. My Test-Device is a Lumia 535.