Please make more use of Spies, right now the only thing they really excel at in game is simply recon, until they're caught.
Espionage and Sabotage need workin' on.
I haven't actually tried Sabotage on a bridge, but that would be interesting.
Assassination, cabinet ministers, even potential leaders, purely affecting relations mainly, giving provocation for war, WWI obviously. Maybe the introduction of a leader unit that has no real function but to be stationed in a hex. It would be a target for all intents and purposes, it could have a production bonus modifier to increase output around it, that way it might make sense to go on tour with it, or even a relation modifier if you have a transit treaty with a friendly, or allied nation.
Espionage, set law enforcement to 100, build a security bureau, and voila no need to worry about partisans/spies...c'mon' now
Relations need work in this game too, literally this game is all about money, and while throwing said money helps gov-gov relations, the populace still doesn't budge in their opinion normally.
I feel like the funding a supporting government, or funding revolution, aka opposition, encourage independence etc. has really no impact save relations, it does seem to make a funded government like you after a while, but that is no promise to the populace, and I can't recall it causing any revolution or declaration of independence for any colony that wasn't already going to do so regardless.
Now, I don't know about anyone else, but playing as the Empire of the Rising Sun in a WWI setting to me just seems like a dream, a golden opportunity to get things expanded in the south pacific before America had too much power their, they should have taken the east indies and new guinea when they took Qingdao aka Tsingtao.