I'd even be happy with an "infrastructure project" that unlocks with each Colony Model/Plan/Blueprint/Grid; a sort of group infrastructure that you can build and it fills in the gaps of earlier era infrastructures.

Alternately, when you unlock Colony Model/Plan/Blueprint/Grid, it unlocks the empire ability of "Modify pre-[Medieval/ER/Industrial/Contemporary] infrastructure cost by -20%" (cumulative).

I believe this should not be added, because it will cause huge imbalance in city gameplay. I mean, you will mostly build only quarters, as you know that in next era, all infrastructure will be build for zero cost. So, now this system is already convenient, as by the time you open colony model, you already have cities with enough production to build any infrastructure you need (and until that time you have to choose wisely what building fits your current strategy). And in new cities you don’t need to build anything old, so you can focus on districts and new infrastructure. The exploit with ransacking old city is usually punished as you mentioned with population reduce to zero, so I think it is better to keep as it is looks like now

EsoulBoy wrote:
I mean, you will mostly build only quarters, as you know that in next era, all infrastructure will be build for zero cost.

You know, you're right.  It feels a bit slow having to build all that infrastructure, but it is fairly balanced.  Capturing/assimilating an Independent People's city sometimes feels a bit like cheating to get a free city; it feels natural to have to put some production and money to bring them up to the level of sophistication of your own empire. :P

I don't like the idea of doing it with a button, but I wouldn't mind this tech unlocking a special project that groups up all the missing Infrastructure from previous era and allows to build it all at once at a discount.

That being said, I think either game got balanced better (for Endless speed I play on) or it was healthier to my playstyle to take those couple months of break, because this playthrough my city queues didn't lag pretty much all up until it was time to start railroad connections and National Parks (at which point any build order promptly went out of the window).

Actually, at the time they appear, you have to found new cities (as there new city caps appear), and assimilating/conquering city is not always an option, so it is okay with timing they appear. Talking about their purpose, they found city without using influence, which means you save influence by using production, or if you have many influence, and it is hard to bring there settler, then you can use colony plan. But can’t disagree, that I rarely build them… It is common for many units, I hope some of them will get new opportunities with new stealth system, but actually they could be more useful, if they add some peasants/militia to your new city, so if it was far away, then you can disband them or protect new territory from native independent people of that land. In such way it will be not only matter of choice between production or influence, but also some human resources above