Thank you for taking the time to answer our questions, Sulla. It is really nice and helpful to get information and insight from someone who obviously already understands the game very well.
About the city flipping: I think I will turn it off completely or turn it on in wars, because I find it strange to have different culture flipping rules between a captured city and a home city. That just doesn't feel right for me, it feels a bit gamey (and it is important how a game 'feels'). It is good to know that strong culture pressure still is a problem for a city even when culture flipping is turned off. So in a game with no culture flipping, culture will still be very important (also for the defence bonus of cities). And if culture flipping were enabled in war, than with the new culture flipping rules, you'll still have some time before it flips. Also the worst problem, losing the units, is gone. I'll play a game with the standard rules first of course.
It is also nice to know that there is a pregame option to turn off city razing. I like the many options to fine tune the game before you start. The customer is truly king in this game.
One additional question, it is probably a difficult one.
According to what I read in previews (and some forum discussions about these previews), you can't infinitely expand in the beginning of the game because of the city upkeep, but it is possible to maintain a large world spanning empire in the end of the game. This probably has to do with the buildup of infrastructure (terrain improvements, health/happiness improvements and resources, courthouses, marketplaces/banks, etc.) and the development of the right civics and maybe some other things that get enabled by certain technologies. Also the resistance of the more efficient smaller nations is probably not easy to overcome (at a difficulty level that is challenging for the player, clearly noble is not challenging for you

).
Now imagine that you play a game with totally no enemy opposition, no other civilisations, no barbarians, no wild animals, no opposition to stop your expansion, except for the city maintenance (yes I know, boring...., but it is just a theoretical game

).
At what point in the game would it be feasible to maintain a world spanning empire for you? I don't mean the moment that it becomes profitable to do so, but the first moment that you could build such an empire that doesn't go bankrupt while running 100% tax. With point in the game I don't mean a year, but more a general indication like late renaissance or early modern age.
The second question is: at what point in time will it be economically beneficial, meaning that every city produces more in science+commerce+culture than it costs in maintenance.
I know that removing opposition removes the usual opportunity costs of expanding your empire and thus moves the date that such an empire would be possible far ahead of anything possible in a typical game. But I ask this question just to gain some insight in the underlying city maintenance rules. In a normal game, the costs of expansion compared to the relative low value of the added cities will cause you to try to improve your empire in different more lucrative ways.