Well, both money and population are a problem for many factions in the early stages of the game, but it is also widely agreed that this early "uncertain" phase of the game is short enough already. I would be concerned that the only effect this kind of addition would have is to make the pre-empire phase of the game that much easier. In the end, a POW function would just be used as another tool to dominate the AI, rather than a historical/roleplaying tool.