So I've gotten it in my head to try one of those megacity ruin worlds I've read about on the forums and after spending the last 4 days trying perhaps a hundred different planet setups and literally thousands upon thousands of rerolls, I've come to discover it's rather limited to what extent you can manage that at this point.
Now, just for the sake of clarity and to head off the obvious comments from people trying to give helpful advice on how to accomplish it, I've spent a great deal of my time this week reading all the forum posts on planet gen and again thousands of rerolls on multiple setups to see for myself (I obviously have no life). I understand the ideal planet setups you should be aiming for, the effect of planet rotation speed on rainfall and the importance of that specific point in particular, and I can say that even a world with 5700mm rainfall with otherwise optimal settings doesn't change anything.
The point is that I've found the most densely populated pre war setup you can reliably get is between 10 and 10.5 billion which seems to act as a soft cap. It's possible with enough rolls or just plain luck to get a little over that, but it's increasingly rare the higher over that point you go. I've managed to hit 12.1 once in my thousands of rolls, and then 11.9 last night but those are outliers and seem to indicate where the hard cap actually is. As a quick addendum to this, I have actually managed over 12 billion a few times outside of this, but only with high 90% agriculture worlds with a minimal number of ruins which has been posted as a potential bug and the lack of ruins defeats the purpose of what I'm after in the first place so I ignore those results for what I'm after here.
I understand that it used to be possible to get worlds with upwards of 20 and even 30 billion people, though that was apparently the result of a bug that's since been patched out but I saw a comment in that thread from Vic where he was intending to patch it back in through more legitimate means but it appears that it's nowhere near those previous numbers.
I also understand that it shouldn't exactly be common to see worlds like that, something else I saw Vic state at one point, but truthfully I'm not sure I agree with that statement. The reason cities like New York get as big as they do is because they can have all their food and goods shipped in from elsewhere. If you were to have a sector or quadrant capital with perhaps dozens of specialized planets to keep it fed and supplied then it's not hard to imagine a world much more heavily populated than our own currently is.
Perhaps with the addition of planet classes and the option of choosing the types of conditions you want your world gen to meet for you, one of those options being for a sparsely populated world, then perhaps an option for a major megacity world to be included as well? The randomness of the game is one of it's drawing points but sometimes you get an itch to play a very specific kind of game and I've now spent the better part of a week and again thousands upon thousands of rerolls trying to get something I like over 12 billion prewar for the ruins but just can't seem to manage one I like. Having a setup option to spare me this tediousness would be a godsend.