I doubt off line single player campaigns will ever be able to compare to the immersion of an online war. It will be years before the AI can be developed in any sim to match the skill and cunning of real pilots and the ability to communicate with them realistically. That said if the development can improve the AI, and aspects of the use of Triggers, campaign builders should be able to make some very interesting missions in the not too distant future. All is not lost yet, just because the developer mentions that they will make an MMO with the new IL-2 engine doesn't mean they have stopped work on the single player uses for the game engine. Do some MMO's use AI units or are they all human players? Not knowing if your confronting an AI or human opponent can introduce some element of apprehension of which strategy of attack one would use.
I would say just the opposite, it will take years of practice for a single multiplayer campaign or online war to come close to being immersive or historical. People will not create/fly scenarios that doesn't give them the advantage, and when people are grouped together, they become even more stubborn in their resistance. (take for example, both sets of the Multi-squad campaigns in CoD, I was confronted by my own squad who was running it for providing Radar intel to the RAF, in lieu of the broken radar we had in game, or the RAF's refusal to sign up currently, since their IIa's are no longer uber-weapons.) You cannot achieve any historical accuracy (immersion) with online numbers, where will you find 36 Ju-88 pilots and accompanying crewmembers? All you have are human-to-human dogfights, which is not immersive. People also tend to gravitate towards the best current tactics, disregarding what was done in RL or at the time.