It is been a strong couple of weeks for videos of the Rolling Stones performing with pop starlets — they brought Katy Perry out for “Beast of Burden†in Vegas, and Carrie Underwood for “It’s Only Rock and Roll†in Toronto — but last night’s guest appearance was a master bit of casting. As you will have gathered from the above headline, Taylor Swift was the singer in question, and she joined Mick Jagger for “As Tears Go By,†the Stones song that was also a Marianne Faithfull song. This is genius: Not only is Swift the spitting image of sixties-era Faithfull, but she’s already dated the 2013 version of Mick Jagger. Forget the Joni Mitchell biopic, can Taylor just do Marianne? And then maybe a concept album? Let’s really work this angle (except for the drugs. Don’t do the drugs, Taylor.)