@valera-rozuvan and @nedbat, @cahrens asked me to see if I can more elegantly solve the original presentation problem (hiding the full screen UI button for Video Alpha components only when displayed in Studio). 

I believe if a presentation needs to be changed for a user's experience within an app (Studio in this case), its that app's job to account for that styling. With that said, I've added a new Sass file to Studio's import stack for use in customizing xmodule styles in Studio contexts. 

This seems to resolve the problem in a more clean and scoped way (though I had to use "! important" in my style declaration due to really bad selector specificity in the xmodule's universal css). Would you mind reviewing this and signing off on this approach? If you approve, this feature flag is not needed and should be removed.