I don't get the point of this, you get pretty much the same thing by doing nothing. Fix the menu to the top of the page, when you scroll down it goes away, scroll back up and there it is. Almost no one is going to care that they'll need to scroll back to the top, I'm sure of it.
Because apparently we've run out of hard problems to solve in computing (as demonstrated by the amount of useless stuff we create) and need to think of the next UX trend that will give our users 0.0001% more satisfaction and increase productivity by 0.000009%.
I don't get the point of this, you get pretty much the same thing by doing nothing. Fix the menu to the top of the page, when you scroll down it goes away, scroll back up and there it is. Almost no one is going to care that they'll need to scroll back to the top, I'm sure of it.