With this rare opportunity to recreate AE from the ground up, it's a good time to ask some deep questions about what direction we want to move in for the future. When working over the design, I ran into a conundrum: should AE fundamentally be a airline business simulation or an airline scheduling simulation? Right now we're in the middle: the demand and pricing model lacks sophistication, and there are no timetabling or maintenance details. This keeps the player's workload relatively low. However, if we add many features players are requesting left and right, the game's complexity rises quickly. Players who are more interested in the business/competition side could get turned off by the micromanagement involved in scheduling flights (especially with timetabling), while players more interested in flight schedules and fleet management would not appreciate the more complex market research and revenue management getting in their way.
I want to put forth a proposal to redefine "multiplayer" in terms of AE: allow an airline to have two or more roles filled by different players. For example: one player focuses on researching markets, deciding what routes to fly, and what services to provide at what prices, while a second player orders aircraft and optimizes flight schedules to meet those demands. Dividing the labor in such a way would (1) allow each player to focus on his area of expertise and (2) allow a greater depth of gameplay without adding too much complexity for one player to handle. Of course smaller airlines could still be handled well by one player.
Furthermore, if we remove the need for each player to have at least one airline to himself, this may lead to a decrease in the total number of airlines. A large airline could conceivably have 3-4 managers under this model, while a smaller airline would have 1 or 2.
Managership under this model need not be all-access. From a technical perspective, it would not be difficult to set up a permissions system where each manager can only access certain parts of an airline control panel or perform certain actions. But from a human perspective, "ownership" of the airline would be more complicated.
Conflicts of interest can be solved by limiting each player to managing one airline in a world. Or allow airlines to specify whether managerships must be exclusive in that game world.
Obviously, teamwork at the airline level would need a lot more details to be fleshed out for it to be a feasible idea. I'm just throwing this idea out there to see how many people would be interested in multi-manager airlines.
Finally, this change would induce a lot more interaction among players (as collaborators!). Then again, not all would agree more social interaction is what we need...