I can't imagine getting sued if we wrote scripts or something.. If they were illustrated then I could see that being a problem.. If a collective group made their own Iron Man comics, it would undermine their product. I don't see Marvel/Disney taking too kindly to that.
I do like the idea tho.
If you just write "fan fiction," you're probably correct. While technically, Marvel could bring legal action, as they have suffered minimal damages, it wouldn't be worth the hassle.
On the other hand, if the comics were illustrated and took away from the sales of the original Iron Man comic, they may bring action against the publishers. While "fair use" concept allows some fan fiction, the moment it detracts from the original, fair use goes out the window.