I found this interesting information on Wikipedia:
Lucas has hinted in the past that he will release his definitive (often called "archival") editions of all six of his Star Wars films on a next-generation home-video format in 2007. This release would coincide with the 30th anniversary of the Star Wars saga. It has been speculated that he will take this opportunity to make any final adjustments, changes, additions, and/or subtractions to his films for this final release. An altered clip from The Phantom Menace included in a featurette on the DVD release of Revenge of the Sith (in which a computer generated Yoda replaces the original puppet) appears to be a sign that the "archival" editions are indeed in the works.
It is said that this edition will be released in a "Grand Saga" box set. Lucasfilm Vice President of Marketing Jim Ward confirmed that in this final release, Lucasfilm is likely to return to John Lowry to do even more work on the films (possibly digital contemporization of the original trilogy). He says, "As the technology evolves and we get into a high-definition platform that is easily consumable by our customers, the situation is much better, but there will always be work to be done."
Producer Rick McCallum has also explained that Lucasfilm has been holding back a large amount of bonus material for this release, including deleted scenes, as well as numerous previous Star Wars "making-ofs," spin-offs, television specials, documentaries, and other special material.
There has been much hope for another Star Wars trilogy but George Lucas has said that there are no plans for episodes 7, 8, and 9.