Here's another concept: implementing Mutual Assured Destruction in Civ 6. When there are X number of nuclear missiles present in the world, then the first time any of them get launched, the game enters MAD Mode. In MAD Mode, all players give orders to their nuclear arsenals. These commands are then enacted simultaneously, resulting in a nuclear holocaust. Then the game ends and the winner is determined by score. Obviously the scores will be affected by the apocalyptic devastation of MAD, so choose your targets wisely! Destroying enemies' Wonders and population centers goes the longest way towards reducing their endgame score counts. This would add a ticking time-bomb element to the late game. Will you be able to launch that spaceship before the nukes start flying?