You can do that in FSX, but FSX is basically only uneventfull flights
I agree i'd like that even if, like you, i like difficulty.
and it definitly should'nt be too hard to implement using tracks
But it had a bad side effect on me with Silent Hunter serie, since you can save anytime you want, sometimes i can't restrain myself (when you have been scanning the blue for 2h without spotting anything) from saving just before i fire a torpedo, and i reload if i miss or if something goes wrong...
it's completely my fault but it does remove a lot of the fun too...
-go to intercept a convoy
-save
-approach without being seen (reload if wrong interception course)
-save
-fire torpedo (reload if missed)
-save
...