One-Sided Embargo's are exactly what they imply. You are able to control what Civs can have trade routes with you. This ability could be unlocked at Currency in the Classical Era so you won't be able to screw up the others early game or vice-a-versa. If you won't allow a specific Civ to establish trade routes to your city, you will face a diplomatic penalty. Why this could be a good addition? Well, trade routes give a bonus to tourism(25%, does it change based on number of trade routes established or if both sides have trade routes to the other civ though?) and is one of the few tourism-boosting action that the player doesn't have control over (besides great works if I'm not wrong). More so, it can affect other Civs to have a revolution and change Ideology, not a desirable thing if you want to worsen your relations with a specific Civ, or want to them to build the Ideology-locked wonders. Tourism isn't always a desirable yield. Great Works, Themed buildings produce it and you have no control over it. One way to go about it is to add an event that could remove the tourism bonus from the slots of the buildings and change it to gold instead, proportional to the number of slots. It could be viewed as restricting entry to foreigners by raising the entry fee or whatever. On a side note, can you sell the free hotels given by events? Lastly, is it possible to add more tenets to ideologies and more reformation beliefs? There are so many things that could be added for a more flexible play-style.