At this stage of the game, it certainly seems like a bad with the Flaming Lips' following is too big to open for anyone, but of they haven't reached the mega-stadium level of Coldplay. That's why The Flaming Lips will be opening for Coldplay for a few dates of their European tour later this summer. Other artists inlcude Bat for Lashes, Jay-Z, Girls Aloud, and White Lies. Coldplay must be pretty confident in the level of their stadium spectacle, if they're comfortable following all of these other performers', well, stadium spectacles.
More details and the full list of openers here.