So, after playing a huge multiplayer map with 3 humans and the rest AIs I have come to the conclusion that the number of trade routes you can establish are very clearly based on a 'small' sized map; in a game with a possible 8 trade partners (after several were wiped off the planet) I've got only 5 possible trade routes going into the Industrial era.
This causes several problems; the most glaring being they appear to provide a static quantity of gold... so if you're on a huge map where the massive swaths of land will support 12ish cities easily, 5 trade routes isn't supporting that number of cities.
I pretty much feel the number of routes being tied to tech unlocks is wonky and doesn't feel right at all - personally I think it should correspond to something more relative to the actual size of your empire. Like the number of cities - make a building that each city has to make to open a route for it and then build the caravan. It's really the only realistic way to scale given the ability to create any size map with scripts.
This causes several problems; the most glaring being they appear to provide a static quantity of gold... so if you're on a huge map where the massive swaths of land will support 12ish cities easily, 5 trade routes isn't supporting that number of cities.
I pretty much feel the number of routes being tied to tech unlocks is wonky and doesn't feel right at all - personally I think it should correspond to something more relative to the actual size of your empire. Like the number of cities - make a building that each city has to make to open a route for it and then build the caravan. It's really the only realistic way to scale given the ability to create any size map with scripts.