I remember advocating for espionage in GCII.once implented, it just didn't mesh with the rest of the game.
Of all the features mentioned, I would put it on the bottom of the list.
^^^ Well one thing I miss is being able to get techs I dont have during invasions. Also being able to stop or slow another ai's tech lead can help out. I'd like a system that gives us a chance to steal techs.
add heroes. spies, admirals, actual governors whatever and flesh out things like tech stealing, diplomacy, etc through abilities they can gain. doesn't all have to be in the tech tree. I do miss having more stages of weapons (and thus more variety in the battle sequences) from galciv2. and death stars of course.