Someone should write the vatican about this, and since there is a new prefect of worship, you might get an answer. It COULD be that this question of projection screens was partly anwered when the question of whether priests would be allowed to their ipad on the altar was proposed - as far as i know it was a no.
Hmm....it seems DMS 72 allows extraliturgical audio devices (autoorganum, grammophonium, radiophonium, dictaphonium seu magnetophonium, et alius eiusdem generis). DMS 73 forbids projectors (machinarum pro imaginibus proiciendis, praesertim vero earum quas cinematographicas vocant).
So it's not clear if, for example, LED screens are forbidden...
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