1. I like multi-human on multi-human fights. I don't have an interest in flying around unopposed on a terrain or flying against AI. That's basically single-player stand-alone gaming and is vastly inferior to multiplayer gaming. I vastly prefer many-on-many to one-on-one fights. I.e., single-player = 1 on fun scale; one-on-one = 10 on fun scale; many-on-many = 100 on fun scale.
2. Just about anything can be done with today's technology.
3. You probably can't keep a player interested forever unless that player is me or 715b. We are the only ones I know who are still playing AH and AW before that from the late 1980's. Most people, at some point, drift off. That is because they are weak!

It seems that keeping the game up to date and folding in occasional user input on changes here and there helps keep people longer. So do squads, community, and (I hope) special events. Scenarios are what has been my main motivation since the mid-late 1990's.
4. Flight sims are niche play compared to the whole world of gaming, but not a small niche (considering the various WWII aircraft games these days).