This “surprise announcement” (very vague) will either be the unaltered versions hitting blu-ray at long last or have nothing at all to do with a re-release of the movies.
But, as i have said before, there has been nothing even mentioned about a “surprise announcement” happening at Celebration. It’s just something that has been twisted from the official announcement of the panel.
The only two official things said about the 40th panel that mentions anything about “surprises” :
Official Star Wars site:
…this marquee Celebration event will undoubtedly include many not-to-be-missed surprises.
Andi Gutierrez on the Star Wars Show:
Celebration is the place for surprises, make sure you attend this event. That’s all we are going to say.
NOTHING about any announcement being one of the “surprises”.