They might play it. With all the petitions and all they might find a way to play it. Also, if they plan to release they shows on itunes, then there is a bigger chance that we´ll get it on tour. Many bands play never played before songs on their current tour when they are selling all their shows online. They do that to make people want to buy the concert even if they didn´t assist. For example, Metallica released livemetallica.com, last year, where they sell almost every show of the 2004 tour. They played a lot of rarely played stuff, including a song that was never played before because they used to say it was too fast and hard for them to play (Dyers Eve), but the fans had been requested this song since 1988 when it was released. And they finally got it, almost 16 years later. U2 could surprise us the same way, and signing the petition can only bring more hope, and it doesn´t do any harm.