Situation:
Currently, each colony gets +1 (unlocked) building-slot per +5 POPs ...
Problems:
01. You have to wait for +5 POPs on a colony ...
02. You have to resettle 1 (unemployed) POP from colony B, 1 from C, 1 from D, 1 from E and 1 from F to A in order to have +5 POPs on A ...
03. You have to repeat point 01 / 02 until all building-slots on a colony are unlocked ...
05. You have to extend point 01 / 02 / 03 to all the other colonies ...
06. City-districts, housing, infrastructure ? PFFF ! Just be fruitful and multiply my little sweethearts ! ...
07. placeholder(s) ...
Opinion:
Instead of POPs, it's better to unlock building-slots via housing ...
Reasons:
01. Since you're able to queue the construction of districts (the primary housing-source) and buildings (a secondary housing-source), it would be possible to minimize the buildup-process of a colony into a 3-steps-one (01. Queue and wait for the construction of the districts, 02. Queue and wait for the construction of the buildings, which provide additional housing and 03. Queue and wait for the construction of the remaining buildings). The current buildup-process of a colony plays more like a 15-steps-one since there're 15 (not 16) building-slots to unlock (since the first one is already unlocked for the capital), so that you only construct a single building every time you get +5 POPs ...
02. Basically, this concept (in favour for housing) would work identically like the original idea of the devs (in favour for "infrastructure"), that way more unlocked building-slots are provided by way more city-districts (instead of (for example) way more agri-/mineral-/energy-ones). The current approach is, at least for me, way too unintuitive since, especially due to the overpopulation-feature, any colony, even a "dirty" and underdeveloped agri-world (with way more agri-districts than city-ones), is somewhat qualified to unlock all of its building-slots to become (for example) a "clean" and developed tech-world (with a lot of research-buildings).