I suggest that one unscientific way of putting the vulgar second person singular pronoun, you, to the test, in terms of it's use in addressing God in the liturgy, is to take the classic English version of the eucharistic hymn, "Agnus Dei", and imagine just replacing "thou" for "you."
So instead of singing this:
O Christ, Thou Lamb of God
try this instead:
O Christ, You Lamb of God
Obviously the makers of modern liturgy know this is unworkable, so they leave out altogether the opening address to "Christ," and go straight to "Lamb of God." And of course the "O Christ" is a poetic flourish and not in the Latin. Nevertheless, a little exercise like this goes to show the linguistic and aesthetic limitations of throwing in the "you" where we once had "thou."