Personally, I can only see myself playing a multiplayer game if most of the impulse is played by players individually (without the need of the other players to be online) and then all going online only for the interactive subphases (like combat, interceptions, etc). I know that WiF design is not suitable for this, but some workarounds (implemented in the game, or unofficial) could be implemented.
Not having myself a lot of time to spend playing and being difficult to agree with other people to be online at the same time, I don't want to waste it waiting for someone deciding their production lines, moving all their counters around or deciding what units to build at the end of a turn.
Similarly, when I play a wargame, I like to think of the different possibilities of a turn, study them, calculate success chances, review the game manual... before I go with my movement. And this takes time (sometimes a lot). I know I will not do that (out of politeness) if someone is waiting for me online on "the other side of the screen". So, the "online only" game mode, reduces my enjoyment of the game too.
In my opinion, PBEM (or a mix of PBEM and online interaction) is the perfect design for a game. I remember this could be accomplished with AH Rise and decline of the third reich on its PC version. AI could be switched on and off for each player at any moment, thus allowing an offline player to move forward, with the AI taking the interceptions decisions of his opponent. I know, that was a much simpler game, but that happened almost 30 years ago...