I agree that the AI should be held at one of the highest priorities now. Its importance for single-player goes without saying, however I feel that it would benefit multiplayer as well.
Not sure if eveyone is aware, but you can actually spawn with AI wingmen in multiplayer. This is a key feature in regards to helping recreate the sheer number of aircraft that featured in the Battle of Britain - it is impractical to expect to get the same amount of humans to join the one server.
At the moment its not worth taking AI wingmen because they just can't fly properly, on the ground or in the air. Coupled with the fact you just don't have any real control over them and it just turns into a frustrating experience. For the amount of work they put into enabling AI to dynamically spawn with players regardless of the missiontype, it just seems wasted when they just didn't come through with the code for the actual AI itself.
I don't know what the full story is. Maybe they lost the team member who was working on the AI and someone else had to fill in his place. I would hope that now however that they have enough team members working on it to actually get it working within a reasonable timeframe. A significant chunk of enjoyment that someone can get out of this game is lost because of the broken AI.