If you burn a city any tile that city owned that is within 5 tiles of one of your cities (AKA the max range you can own) is added to the closest city you own. If the city owned tiles they never stole, but are still eligible, then you get them too. There is already a built-in ability to work other city's plots, which means that you can already keep the city as a puppet and simply work the tiles with the original city. That means this is mostly a QoL update allowing you to raze and recover your tiles instead of being forced to keep a puppet you don't want. The ability to take one non-capital city scotch-free allows you to do this if you're willing to respond. Thus this solution solves your issues with citadels, people's issues with Washington, and gives a better counter-play reward to forward settling, in a manner that I feel is more elegant and intuitive. (IE it's reasonable to war if someone takes your tiles, so players and AIs alike will overlook you taking a single city to get them back. Also taking and burning the city will refund tiles, which I always feel it should.) I think the option for a trade deal would be even better if it wasn't too new-code heavy because it makes it easier to have a war result of "I got back my tiles and didn't knock the AI out of the game." It also could allow you to steal tiles and sell them back, or demand that your afraid neighbor give you back that tile he stole.