I, like many players would love to see the return of the Military Career, but not as you knew it!

1. Active Career
2. Showing most of it, strictness, courage, sims being away for a while (you don't see them while they are away.)
3. Uniform, mostly modelled on Army career.
4. Marching walking style unlocked at level 2 of career, you are taught to March. You can choose whether your sims obey or disobey the drill instructor.
5. Salute available for military Career people and there kids (for fun) at level 3 Salute with utmost respect at level 8
6. Physical training.
7. Obstacle course at home.
8. If your sim chooses to misbehave at work he could have to do push ups, but 3 warnings/ push-ups and you loose career performance or may even be demoted.
9. At rank 1 when your sim starts, he or she needs to be level 2 Atheletic skill, rank 2 is level 3 Atheletic skill and so on until level 8 where you need 10 Atheletic skill.
10. Your sim must salute higher ups in the military and will call them Sir.
11. Your Sim can do a special kind of Push up at level 5
12. Your sim can get married in their uniform, but dressy uniform. Idea by @griffin1842

Those are what I have thought of for now, if you have ideas please give them to me.