It seems to me that 7 day turns may be essential to make a game as huge as WITP playable.

I agree completly Jive.
We play PBEM UV on a 3 day turn period.It works OK but you have to be very careful if you put CVTF on reaction as you are committed for 3 days.In one case my cv was torped and self detached,then the remaining screen (no CV) reacted next to Jap CVs .OOPS

The UV system needs several extra controls eg:
Waypoints for TF movement.
Reaction ranges
In regard to aircraft i think altitude assignment should not be done by the player.The player should specify the commitment levil eg max effort, harressment etc and allow certain tactics. eg skip bombing,low levil etc for certain missions.
Currently in UV You may want 100 ft for naval attack but 6000ft for the secondary mission of land attack.
WitP is a true Strategic long term game.
Weekly turns MUST Work WELL.