It would make the Strike Fighters series obsolete.
Hmmmm... not quite. For some, maybe yes. But not for all.
The biggest thing keeping me from switching from SF2 to FC2 is the lack of random missions or dynamic campaigns. The first flight sim I had was Graphic Sim's Hornet 2.0. That thing had 28 missions. That was it. And I couldn't have been happier with it. Korea added 28 more. Wow. 56 missions?!?! How could that ever get boring? And I knew every mission by heart...
Fast forward to now, and the bottom line is that WoX/SF2, IL-2, and F4AF have simply set the bar higher in terms of reply-ability. All three of those have dynamic campaigns in some sense. I have FC2 and got to be pretty good with the A-10 in the training missions. I went to start the campaign and got shot down on the first mission by an SA-11. Wait... now what? I just go back and fly the exact same mission and know that the first thing I need to do is hit that SA-11? I just couldn't bring myself to do it. I didn't think it would be an issue until I tried it. I would read through SimHQ forums and think "what's with all these snobs that demand dynamic campaigns?" But then I realized I was starting to climb into the same boat. The bar has been/is being raised.
So for me, the lack of random missions and dynamic campaigns is the one thing that keeps me from spending all my time in FC2.
Plus there is a group of people (what % of simmers, I don't know) that are all about 50s/60s/70s stuff. So, of course, to completely make SF2 obsolete, FC2 would have to greatly expand it's aircraft selection and time frame. In that regard it will never top SF2.
Slightly more on topic, I own FC2, but don't have either DCS title. So if I do want to upgrade it's just the one purchase for me. But I do understand why users would be annoyed that they need to pay for separate patches for each of the 3 titles if they want to keep them up to date. As someone totally unqualified to have an opinion on the matter, it seems like a user should have to pay for the upgrade once, and then it could apply to any module they have. Especially if we're talking about the DCS titles. My impression from the start is that they would be modular and could be simply added on top of each other.
Now, whether that pricing/business model would work for ED is something I can't intelligently comment on.