Mission editor suggestion .
 

Sink x amount of tonnage before convoy reaches x coordinates on the map type
scenario .

Wolfpack Mission Editor suggestion having the ability to have a escort support group coming to the aid of the convoy or single escorts arriving at
different intervals to beef up the escort screen.

I think the most important feature for the mission editor is to bring the detecting capabilities of all the ships as close to (playable) reality as possible. So ASDIC not being able to ping you when surfaced and at periscope depth, maybe radar introduction at the appropriate time, amount of waterbombs, weather and ocean conditions, night & moonlight, random manoeuvres etc.
Whichever scenario is chosen, it will depend on the skill of the player and AI.