I would imagine Heinkel had the idea of designing something to eclipse and supplant the Ju87. After all, Heinkel was frustrated by support for Messerschmitt regarding speed records and always had an eye for performance aeroplanes. However, although intended as a dive bomber (B model) or reconnaisance (F model), it was also put forward as a fighter-bomber (J model). Although pilots reported favourable handling characteristics, the design failed to reach the desired performance and the J model was abandoned. Twelve B0 pre-production airframes saw service for six months before being withdrawn on the eastern front, transferred to Rumania where they lingered on until the mid-war.
I guess the J model remove the rear gunner?
No, I wouldn't expect that, although you could postulate that a particular version was experimentally adapted. So we have the V4 single seater prototype with underwing cannons for tank busting, intended for production as the B4.
The problem is that while the Heinkel 78 had good weight lifting capacity and gentle characteristics courtesy of the generous elliptical wings, it wasn't a small aeroplane, and wouldn't compete on equal terms with single seaters, so a rear gunner is actually desirable.
Well very interesting, thanks for sharing.