Will Superman appear in Green Lantern?

Hi all, this is my first article, so please bear with me- I promise to make it quick.
I was encouraged by fellow CBM-er JorEl77 to expand upon a comment I made in another news piece, one regarding Cavill's sudden casting as the Man of Steel. I speculated that this casting came early to sneak in a Superman cameo to Green Lantern.
If one considers the timeframe of the recent Spider-Man casting, or the Captain America fiasco, the choice of Cavill is indeed coming quite early. Superman is not rumored to shoot until this summer, over the period in which Green Lantern is being released. Green Lantern is most likely still going through post production at this stage, with plenty of time to sneak in an Iron Man-style cameo post-credits or during the film (Personally, I've always pictured the cameo to involve Clark Kent among a crowd looking up in the sky at Green Lantern. Clark merely smiles and shakes his head...).
The thought of a cinematic DC Universe is an exciting one. We came close with Kevin Smith's Superman Lives script, featuring a brief Batman cameo, not the mention the numerous Batman vs Superman attempts. Nolan, however, has remained steadfast in his insistence on Batman existing in his own universe. This makes sense for such a grounded portrayal of the character. Superman and Green Lantern, on the other hand, are fantastic, superpowered beings which could easily reside within the same world.
A Supes cameo was incorporated early on into the Green Lantern script, but its current status is unknown. I believe it was Geoff Johns who joked recently that Tom Welling was welcome to visit the Green Lantern set and do a cameo.
If this does come to fruition, I hope it is done in a subtle manner- like what I previously described, more of a Clark Kent cameo, the brief appearance of Nick Fury in Iron Man. The overbearing "Avengers assemble" storyline truly crippled Iron Man 2, and showed the flaws of a shared universe. Hopefully DC, who are sometimes overly-careful with their characters, will learn from Marvel's mistakes and set up a carefully planned, fully thought-out universe that can retain its integrity.