The discussion I (faintly) remember has happened long ago. A contributor (Bigjoe5
) had implemented a quite complicated scheme where resource/output boni certain techs granted had been based on population and/or infrastructure, depending on what other techs you had researched. The idea had been to offer the player two viable, distinct approaches when developing their empire: either go the increase pop route and base the economy of your empire on high population, or go the "construction route", where you research techs that improve planetary infrastructure, get resource output boni based on infrastructure, basically basing your economy on highly developed infrastructure.
The approach had been rejected for two reasons: first and more obviously, it was too complicated and not KISS. The second one was what is important for our discussion here: It made the game concepts/elements "population" and "infrastructure" too similar, too exchangeable, too less distinct. In FO, we aim for clearly distinct game elements/concepts, because that makes the game mechanics more KISS.
For that reason, there is one, and one element only, that acts as base for resource output: population. Infrastructure is a different, separate concept/element, and therefore should serve clearly different, separate purposes. Using it as a base for resource output boni would go against that principle.
As a sidenote: This is also the reason we changed how shields work long ago. Originally, shields didn't provide a constant damage reduction factor, they simply provided additional structure points like armor parts do.
The only difference to armor had been the way how those additional structure could regenerate: lost structure that has been provided by armor can only be regained by repairing the ship (at an Orbital Drydock), or by the self repairing capabilities provided by the damage control techs - basically the same way base hull structure can be regained (which is how armor still works, no changes here). Additional structure provided by shields however regenerated automatically at a certain rate between battles (usually that regeneration rate was much higher than the self repair rate of the damage control techs). Ships could have several shield generators back then, as their strength would stack like armor does.
That of course had been a much more subtle difference to armor than what we have now. That difference was perceived as not sufficient, so the shield mechanic had been subjected to a major revision: instead of providing additional structure, shields now have a constant damage reduction effect. Which is much more different to armor than the previous mechanic.
We did that because we explicitely want that kind of distinction/difference when it comes to the game elements/concepts/mechanics of FO. And for that reason we have refrained from allowing infrastructure to be used as base of resource output boni, because it would make population and infrastructure too similar.
Of course we can reopen a discussion about that, but there need to be some very good reasons why we should revise that decision and if there is really no other way to make use of infrastructure. IMO there have been enough interesting ideas in the past, we just never got around to actually go ahead with one of them (because there was always something else that had been more important). So I still lean strongly towards keeping that distinction between population and infrastructure.