Interesting drawing. First time I saw it was in Justo's 2014 Ultimate Flying Wings of the Luftwaffe - but this is a 2009 scan of something printed. Was it originally printed in the Reichdreams Dossiers series?
It's a DFS proposal for fitting a coal-powered ramjet within the airframe of Lippisch's Delta VI... so maybe not a Lippisch drawing (he was busy at the LFW in Vienna). It does have the characteristic cooling channels either side of the ramjet 'box' though, just like the P.12/13.
In spring 1944, Lippisch was still planning to power the P.12 with liquid fuel. Within a short time, however, he began to consider coal as a better alternative - resulting in the P.13. Maybe this was the proposal that made him change his mind?