What about all of the earlier Star Wars material that was just drafts and never made it to the big screen?
http://io9.com/5661073/10-things-you-didnt-know-about-the-empire-strikes-back
http://io9.com/5539807/what-did-the-original-script-for-the-empire-strikes-back-look-like
A cloned Lando Calirissian. That just sounds so ridiculous. Thank God these drafts stayed drafts.
Lando was an awesome character in the originals because of what he did-his character, his motivations, his goals, his deeds, and especially the ending of Episode 6. Including him into the prequels would just be shoehorning him into there.
That is one of the reasons why many star wars fans, myself included, absolutely hated the Star Wars prequels. Massive shoehornings of many characters everywhere. Anakin Skywalker built C3PO, about 33% of all of the stormtroopers were the boba fett clones, not to mention the Anakin-Greddo fight.