I know this would be a mess to program and balance, but it would give playing in Slow+ speed more sense. It feels like the AI magically produces cities with districts, and pumps out armies of 4 or 5 units in the fog of war, it's insane. The speed relies heavily on the production queues, so to have a dedicated Unit queue can make for a more interactive and slightly more realistic long games. This would totally give an advantage to militarist cultures, but would also counter the merchant cultures who can buy everything from the middle of the game onward.

One could perhaps have the option to select one or two queues at the beginning settings page, or perhaps there could be a penalty for having the two queues working simultaneosly.