Side shooting CAS aircraft first appeared commonly in combat in the 1960s, with the USAF. Puff the Magic Dragon, or more properly the C47 Spooky, being the common names used. A variety of weapons went on the aircraft, tho high volume 'mini guns' were the best known.
So, what are the odds a similar tactical support bomber might emerge in the 1930s, and how practical would it be in combat in that era & the 1940s? How might it develop?
Given the limited range of the guns, its low/slow attack profile its not going to be a independent attack weapon in many circumstances. Still there seem to be some possibilities with good tactics and support partners.