I haven't looked at the actual code, but it should be possible to port this more or less intact to RFC. If anyone is prepared to do the conversion, that is...
I was more looking to see what could be done within the limits of PyScenario, but thanks for the tip! (I haven't tested RFC:E and didn't even realize there was a Crusades feature.

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I see that PyScenario is much more focusing on single events regarding units and town, to help adding events and creating units or cities (I see it ideal for a end-or-rome scenario with a full grown roman empire and lots of barbarian spawning to destruct the pax romana)
continuing with edit...
It's quite difficoult to code the crusade in a nice way.
Using the PyScenario, maybe we could have:
Check the trigger for crusade event at 1095AD, 1147AD, 1187AD, 1202AD, the dates of the 4 most important crusades.
Other time points (for other 5 crusades): 1217, 1228, 1248, 1270, 1271... but these never even aimed at the holy town.
Search for Jerusalem, check if it's in islamic hands, and create crusaders (military units).
However in this flow there are many failure points like the fact that Jerusalem may be not the Christian holy town, and that we don't know to whom to give the control of the crusaders.
An other way, with more code that is not part of PyScenario:
Check every X turns for Christian holy city
If it's controlled by a Civ which state religion is not Christian then
search for the Christian Civ with the greatest power (not score, but power)
if its religious civic is theocracy, immediately trigger the crusade
else if the civ is human, ask the player if he want to start the crusade
else (the civ AI) 70% to start the crusade if "state religion", 50% with any other civic
Crusade:
Automatically trigger war between the civ controlling holy city and the crusaders' civ.
Create units belonging the to crusaders' civ near the holy town to conquer
Additionally give a % modified by religious civic for each Christian civ to join the "fun".
Honestly, a crusade event is not the simple.
I would like a really general mechanism that can trigger religious wars