One thing that nearly happened a few years ago that would've been BRILLIANT if it had've, relates to when Blink 182 split up.
On their final album, they did a track called All Of This, featuring Robert Smith on lead vocals, with Tom DeMong just backing up. Just before they announced their split, they'd suggested that All Of This would be their next single, and I would've loved loads of Blink fanboys to buy their new single, just to won der who the hell was singing it!
To be a little on-topic, the final Blink 182 album was, and still is, really good. They grew up, they calmed down, they used some weird and wonderful instruments and techniques, they got Robert Smith in, and they generally made some good music at last! Stockholm Syndrome and Obvious were excellent.