That being said. Alan Moore was in the running for rebooting Supes but lost out to Byrne (which is sorta like DC giving Loeb the superman book after Morrison asking for it...oh wait that did happen).
I hear many contradictory things about what Moore's involvement was to be in the Superman books, post-Schwartz.
The version I've heard from Marty Pasko, which is the version I'm most inclined to think is true, is that Alan Moore was brought on by Schwartz to finish his tenure on the Super-Books with a bang, and Moore wasn't going to stay on post-Schwartz. This has the veracity of being from someone that was there, and also it's true: Moore DIDN'T work on Superman after Schwartz left.
The other idea I've heard, more as rumors...was that Moore was going to be on the new incarnation of DC COMICS PRESENTS, a book called SUPERMAN PLUS (insert guest-star here).
Moore left, from what I hear, because he was told to work on Byrne's plots. Which prompted his dry English retort, "well, only if he can ink on my pencils!"
The reason I doubt the veracity of this SUPERMAN PLUS story is this:
1) the only places I see it written about are hearsay. I can't find anyplace that gives Moore himself, or someone around at that time, talking about the project.
2)
DC never did a Superman team-up book post-Schwartz! (Unless you count the brief period when Byrne wrote ACTION COMICS as a team-up book.)
3) The title SUPERMAN PLUS is also attributed to aborted projects by both Neil Gaiman and Grant Morrison as well! This leads me to believe there's some garbled history.
The idea Alan Moore was in the running to try a Superman Reboot is a new one on me, and frankly, I doubt if it's true. I've heard stories from people that were there that say Cary Bates was in the running, as was Frank Miller.
Also, I wouldn't compare Morrison to Moore. For one thing, Moore can do characterization amazingly well...of his generation, only Levitz, Alan Brennert, and Busiek are better at telling character-centered stories. On the other hand, characterization is Morrison's great weakness.