I like the idea about being able to deploy air units.
For Elves maybe Eagles, Gryphons Etc... more majestic birds and creatures.
For Humans maybe objects under inspiration of Leonardo DaVinci's flying machines.
For Orcs maybe War Balloons etc...
But i agree the game loses its appeal after one has repeated quests so many times. Pop Cap reached and never and PvP action.
More quests and challenged would be amazing, and additional expenses in the DOF Store for larger amounts of Crown. as you said having an additional 3rd wall would be great! or even being able to expand outside the settlement furthur.