Poor terrain and atmospheric graphics as well as shallow and stagnant gameplay covers most of it. The plane models are actually pretty good.
I'd imagine something along these lines..
First, keep the current MA's like they are and add a test bed MA where the current terrain engine can be pushed. Allow users to submit objects within certain guidelines to let them do much of the work for you.
Second, add a system similar to WOT where each battle earns exp and credits and ordinance/repairs cost credits. Allow free play at substantially reduced credits/exp per battle. Premium accounts ($15) per month players get full use of current MA setups so those who want the same old same old can continue on without interruption.
Develop Squad Wars arenas. Open to those who worked up the trees. These arenas are player built in that squads can build a base by dropping supplies within reasonable guidelines. Bases are built up by dropping additional supplies. Supplies are also needed to repair damage from attacks. This creates a dynamic arena where squads have something to build and defend. Some reason to participate in the game.
This system gives people reasons to build and participate in squads which are the core of what makes AH great. It's human interaction that makes the game great. Give them the challenge or grinding up the tree for the end goal of building their own piece of the world as well as the the dynamics of diplomacy/war and you will have something. Just a pipe dream though. I'm pretty sure the status quo is here to stay.