So most games I have played with a subscription model or a games as a service model. Have something very particular that Aces High doesn't have as much now. That being regular content updates. Something in the range of every 3-6 months. When games I play though like Battlefield, Elder Scrolls Online, GTA5, etc. They come out with huge updates. I mean like an entire new area of the map to explore or a whole new story line to complete, etc.
This brings people who stopped playing the game for awhile a reason to come back, since there is something completely new to do and explore. Some of these games as well also have mod support. So instead of the company having to pay for the development of a free or paid content update. The players themselves who know about creating models, and textures, sound design, etc. Can make their own stuff. We already have that to some extent with sound packs and terrain editing, etc. It would be an interesting idea though for the company to perhaps think about letting other people make their own aircraft who know how to do it.
It's a bit of stretch but if the creation tools that the development team uses to make aircraft was made available to others. Then the community itself could produce its own content for the game. Of course it would be limited to something like a private server or a test server. It would allow to a certain extent to give a reason for players to log on.
The point is though player made mods and regular content produced by the game developers at regular intervals is the blood that keeps games alive. Some games are entirely only kept alive with a huge player base because of player made mods that add different things into the game. Like with Fallout or Skyrim there's literally a new mod everyday you can add characters, quest, weapons, houses, etc, etc. While other games like GTA 5 have been kept alive with the release of small things like cars in between their larger content updates. For example the next huge update for GTA is a Casino that will release in July.