My $.02 worth...
With the benefit of hindsight a "bullet trap" AT rifle grenade that was at least capable of penetrating the side armour of typical AFV's would would have been useful. I seem to recall reading part of the initial impetus for the development of the bazooka in the U.S. came from a belief that effective AT rifle grenades were to heavy to be fired from rifles so truly effective rifle fired AT grenades may not have been viable (or at least were not perceived to be viable ?) with WW 2 technology ?
Giving every rifleman a basic AT capability that didn't require changing from ball ammo to special "grenade launching blanks" probably would have lead to a modest increase in tank losses in my view. I doubt the course of the war would have been changed.
I'm having trouble reconciling a bullet trap grenade and a HEAT warhead from an overall length and stability perspective. I would think you might be stuck with a blank cartridge motivator...someone with the requisite knowledge want to weigh in?