I understand that 4.0 is a preview release. Eventually I'll change over to it when it's released but in the mean time I'm rather weary of spending time making shaders and other things if it's going to be irrelevant in 4.0.
Example, this scene has a few shaders in it that no longer work in 4.0

Looking at most likely a year or more finishing my current project so it may never become a problem for me, I just cant stand the though of losing all the hours of work on shaders and other stuff if it's going to be nulled.