The above idea is not all bad.
I have another idea on how to increase difficulty OR simply what to do with the Days-Ahead/behind system.
Instead of going further down the Road-to-Victory towards the end of the game by contentious advancements thus getting a lot of days ahead which makes no sense since you be basically 6 men running way past enemy lines all the way up to encounters that you are historically not suppose to be at by that D-Day time line.
How would a possible single play of 300 strait fields in a row to the end make sense. It would be D-day + 299 and that sounds very wrong.
Here a solution.
Instead of getting days-ahead of schedule “continuous play = further advancing” does not bring you deeper into enemy territory where you are not normally suppose to be but rather you Take-On-another-Objective.
Basically you go and steal some other squads daily advancement goal.
To put it into a map like view. You do not go further into enemy territory but rather along the front line every time you keep advancing.
that could work, or Do a Capture Ground by Day to Objective, So Every time you push up, You get more difficult, But you work Towards a Goal, every time you Make it, You Move up a zone on the Map of the War, So say D-Day beaches, to the Forest, To the outskirts of town, Have it be like 200 Rows then Capture the forest. Mind you every field is short, so lengthen them or add Traps throughout the map, Hidden Enemy patrols, Bosses, Minefields. Put a Fallback command in, so if you almost lose your Sqaud you can Fall back to the last Zone? Make it So we Are pushing back into Germany in some way idk. another suggestion from reading your post, again no judgment, love what ever you come up with and how the game has been
or like you said, you have to take on the objectives on the Beach, if you go your so many fields, you move onto the next objective on the beach front, put in like 5 then make a new zone, or a push forward like you did in recon and mnb3? i think
Thanks for the feedback.