So far, after two marathon immortal games with BNW, (Venice and Carthage), I quite like the aggression level. it seems more sensible, and I get the impression a lot of it has to do with the map size, resource density, victory conditions and civ/city-state ratio. Most of the AIs that are being passive, are generally doing it at the same time as me. This leads me to believe their behavior was toned back from going power mad with their difficulty bonuses to actually following the same trends in the tech tree as the player generally does. They just do it all better.
Course that's only two games, but in the last one, 6 civs lost their capitals by around medieval era, 5 of those had nothing to do with me. I did invade the ottomans below me, they had been playing passively, as a lot more civs do now, I won't deny that. curious as to why that might be I was looking around his cities' buildings and improvements, he started on the bottleneck of a jungle peninsula with two religious city states on it, me being the closest civ, and until then being friendly and non-threatening. He had founded his own religion, with cathedrals, pagodas, worked jungle culture thing, all his cities had monuments and amphitheaters. The one person next to him (me), was friendly, and on the edge of a desert with a ton of production.
If I'd been in his position I wouldn't have done a single thing differently, he was going for the best option he had, and it would have worked out great for him had he not died.
I haven't analyzed anyone elses behavior and position quite so much yet, but I get the feeling that if you did, all those 'overly-peaceful' civs would make sense. All the new peaceful alternatives to everything make non-aggression, not just viable, but arguably entirely expected and superior, with warfare being secondary to accomplishing the former's goals, which is how it should be. Vanilla, especially, was pretty much just a convoluted RTS it was so focused on warfare, These peaceful civs are just a by product of the game fleshing out the other aspects.
Though it's possible I'm giving the AI too much credit, again, I'll need more games, but I get the feeling this is intentional and really good for the game.
P.S. the moment I took over the ottomans, claiming about 4 times the area of land as any other civ behind a bottleneck I got DoW by every (13) other civ, around 8 of them backstabbing me. So maybe that's another reason the AI hesitates early.
P.P.S Both games I lost due to just falling too far behind economically, despite doing well militarily.
I get the feeling I've seen that screenshot elsewhere by someone being told to stop posting it as they had apparently been posting it everywhere.