And, well, nothing happened. 75 end turns later, I claimed my victory.
I didn't try very hard to micromanage the culture values, but they came out just about perfectly anyway. Thebes and Giza went Legendary on the same turn. Memphis got four Great Works and overshot by just three turns.
Cultural Victory in 1806 AD.
So there was more land out there. I'd wondered for a while but had no need or capacity to go look. I had even wondered if there was another civ; 9 is the usual complement for a Large map, but never know if Sullla pullled something unusual or if Tectonics might even have a different number.
Yah. Good thing Ragnar was so easy to manipulate to Friendly. That "never attack at Friendly" rule is a wee bit abusable. Ragnar could have sneezed me off the planet anytime he wanted. There's something to be said for world-simulation plausibility and playability in a Civ game -- the military gap between the United States and Canada is something like that magnitude but the US would never actually attack. But that leaves the gorilla idly standing by while his buddy just wins the game.
Sullla said "some large AI empires" would ensue, which did come true - Scandinavia and Inca had lots of land in the region south of the player that we couldn't claim. But my game ended before that size amounted to any threat.
I pity anyone who didn't make themselves Ragnar's BFF in this game. Cultural victory might be easy and fast, but it's sure as hell boring. Perhaps somebody else will have a more interesting report than me.