One easy way to implement that is to add a “Kingdom Chest” button to the Kingdom screen (the screen with Explore, Quests, Challenge, etc). That brings you to a screen with Gold, Glory, Gem, VIP chests which require 2 keys to open, or double cost. So if you had 50 gold keys you click on “Silverglade” on the main map, click “Kingdom Chest” on the menu, click “Gold Chest” and open 25 of them which contain mostly Silverglade commons, rares, and the normal assortment of stones and other rewards. If you want more, they are 600 gold each. Likewise Glory Chest would be 40 glory each and Gem Chest would be 20 gems each.
Then anything in game that rewards an Event Key instead gives 2 Gem Keys and take Event Chest out of the normal line up.
I know I’d be willing to expend double resources for a more targeted style option. They would follow the same rules as current Event Chests, Legendary and Mythic are kingdom specific while others are “heavily weighted”. Could even make it 5x cost, while the Kingdom of the current event is only 2x so there is still incentive to wait for the kingdom to be featured before using.
Sorry for going so off topic! Reposted to new thread - Kingdom Specific Chests