I really think the best way to solve this would be to allow communist governments to rush with gold. Or maybe half gold, half population. Maybe have it set up so that one pop point is used up, but the rest is paid in gold. Part of the problem is that once communism is available, most units cost 3-6 population points. I once rushed a factory at a cost of 8 pop points (the city was surrounded by railroaded floodplains) just before I switched to democracy. While the rest of my empire was in WLTK days, this city needed like 5 entertainers just to keep out of disorder for the next 40 turns. 40 turns is a very long time in the late industrial age.