One way to keep things interesting would be faction or faction block specific events. Take the "Gunpowder" event. There could be different events triggered that cover different factions. There could also be prereqs for each.

We could have a trigger of "Search for immortality" that can be triggered once per game. This would have an equal chance of being applied to "Greek", "Egyptian", "Congo", "Inca", "Indian", and "Oriental" factions. Which ever one gets it would then have a set of subsequent events all dependant on "Search for Immortality", to include their initial development of Gunpowder.

Other faction blocks would have contact with a "Gunpowder" faction block as a prereq for getting the event themselves.

That means you could have European knights facing off against bear warriors who are throwing exploding clay pots at them. Or you could wind up with a technological backwater in Europe being invaded by steel clad Aztec troops.

This would require a LOT of reworking on the buildings that are available and when they become available. Advanced farming would be available pretty early on to most factions besides "Greek" based once and all factions besides the "Inca" ones would have access to both Cavalry and metalurgy, at least in a historical game. This would require at LOT more building options and a lot more unit options.

It would be kewl to have Inca deer riders attacking China, firing their long range muskets at the club wielding locals...