I don't know if this has already been suggested but here goes....
Extra historical battles would add an exciting feature to the game. In the sub-mods section there is already a mod that adds the battles 'Siege of Minas Tirith' and 'Seige of Helms Deep.'
The Last Alliance would be very exciting to play and there are many other battles that would be interesting to play.
This could be epic with 10000+ on the field which would be properly scripted. Making the scenario in custom battle just isn't the same as the AI is unpredictable.
I have tried making a Minas Morgul battle but it completely failed however, I am sure someone would be interested in this and giving it a shot ?