So in principle there is no reason the Hetzer could not fill the StuG role, since the long term plans were to replace all PZ-IV/III/StuG production entirely with models of Hetzer. Still not clear on the roles. Going on Manstein's StuG plans, I would have expanded Pz-I production to thousands prewar to build up panzer forces.
Come wartime , I would have converted them to PzJager role but sunk Infantry guns into 1/2 these chassis and 37mm Pak into the rest. After all these are all routed in the mechanized gun concepts of the 1920s. [200-300 farm tractors with either 37mm PAK & 77mm Infantry guns]