Yeah, but then I wouldn't know what to make up, because the Sharingan can pretty much everything already! *whines*
Well... I've thought of both possibilities really. I mean, in the AU of the AU, Zack still leaves the clan (in the process changing his clan name). And, he probably does it early enough that Itachi doesn't even remember him as being Uchiha, seeing as Zack wouldn't flaunt the fact. Whether they meet later and Zack acts as pseudo older brother or not is something I'm debating. Cloud would, of course, be guardian of Naruto.
*laughs* I can totally see Kakashi having a secret crush on Cloud... and Zack trying to fight him off. Aeris would have a bunch of fanboys (OMG! Gai would totally adore her!). Gah!