I used C# develop a WP8 app. I'm wondering if the Windows Phone 8.1 SDK supports WinJS? I saw there are some news that windows phone 8.1 start to support WinJS
If so, I will move to WinJS for WP and WinRT both.
Your comment welcome
As of February 2014, there is no official documentation available currently on Windows Phone 8.1.
So, any comments here would be speculative or based on confidential/leaked documentation. I would suspect that your question will be answered at the Microsoft BUILD 2014 conference in April 2014 (either confirmation or that it was just a rumor).
Given the information disclosed, you might also consider that WinRT applications would be possible on the Windows Phone 8.1+, which would mean that you could write a Win 8.1 Store application using C# and XAML that would run on both platforms. So, switching to WinJS might not be necessary if you wanted to continue to use your core XAML and C# skills.