Well, with the zoom function, the lack of IFF shouldn't be too much of a problem. I know, it's not realistic, but because of the difficulty in seeing aircraft that are less than a mile away, I still use it a lot, and it is fairly simple to tell a MiG-21 from a SU-27 from a F-15. Now, on servers where everyone gets to fly whatever they want, this will be mayhem, but on servers like Blue Flag or strict MiG-21 vs F-5, it should be no issue.
I would like if they put IFF in the fighter, but I don't see it as a big problem without it. I prepurchased a while ago, and the only thing I'm less than happy about is the wait. To be clear, not complaining - I'm just admitting that I'm impatient to fly this thing! :)