If you write your Xamarin Forms UIs using code, then I think you'll really enjoy my LiveCode IDE Extension for Xamarin Studio.
It is now able to display any Page derived class and updates that display as you edit code.
I made a video demonstrating this ability - pardon my stammering as I confuse myself over the .Forms API :-)
https://www.youtube.com/watch?v=5gKv71tVvuc
(Sorry, couldn't get the embed to work here.)