On the System Summary screen you can see the FIDS generated by each planet taking in account number of population. I think FIDS output generated per 1 population (as for not colonized planets) would be much more use-full here.

When I go to system I want to know what can I gain/loos by moving population from one planet to the other. I already have a sum for the whole system in the top of the screen.

The information how many production i get per population on a given planet is not easy to reach right now because it is a sum of several values presented on two separate pop-ups (planet type + anomaly).