Personally, I have no interest in seeing someone, anyone, sign with the WWE as a high priced free agent if they are not planning to stick around for an extended period of time. It has absolutely no appeal for me to see Sting appear in the WWE at this stage of his career, whether it be to face the Undertaker at Wrestlemania, or to be inducted into the WWE Hall of Fame. If the Undertaker/Sting "dream match" could have happened a decade ago, it may have been interesting, but at this stage of their careers, I would rather not see this match ever occur. Plus, Sting has no business being inducted into the WWE Hall of Fame. Strike this name off the list of desirable free agents if you ask me.
Not too much interest in seeing Goldberg either for largely the same reason. Past his prime, won't be sticking around in all likelihood, and personally I couldn't care less about the WCW-theme which is allegedly going to be associated with WM27. If they want to induct him into the Hall of Fame, that's OK because he spent some time and wrestled some matches in the big leagues already. He doesn't need to wrestle this year, just induct him, if that's what they decide to do, based upon his past accomplishments, not based upon a trip down memory lane this year.
Booker T, Scott Steiner, Kevin Nash, Scott Hall, I have no interest in seeing any of them compete this year. The Hall of Fame could be an option for several of them, but no need to fill the WM27 card with legends and has beens, when the depth of their roster is as it is.
Hopefully, there'll be no Brock Lesnar this year either. After the way he left, tanking his match against Goldberg in a terribly disappointing display, he doesn't deserve the big pay day this appearance would earn him. Thanks, but no thanks.
Batista would be a free agent I wouldn't mind seeing return. After his hiatus, he may be interested in coming back. A return of the heel version of Batista, who likely would stick around, that would be appealing. A return of Chris Jericho would be nice too, as would a return of several injured guys (not free agents I realize) such as Christian, Evan Bourne, or Triple H (some of whom will likely have returned before this).
I believe the roster in WWE these days, with the potential feuds brewing, is solid enough to put off a successful Wrestlemania 27. They don't need nostalgia, as some organizations do, to sell this card.