bro i think that's an awesome idea that i've thought of doing myself. but i think the thing youd need to concentrate on is remembering the song. i find when i write songs IRL i remember them gud as if i play them. for example ill get a melody when i'm in bed but if i dont play them on the guitar then i forget them. coz i memba what frets etc so mayb giv it a play in the dream. make sure you really remember it. mayb even try autosuggestion in the dream saying youll remember it when you wake up. otherwise it's awesome idea but yea just have a plan before you do it to avoid being pissed off when you wake up haha