Wow. If Myspace make a come back, it will be like a fight scene from a James Bond movie - completely knocked about all over the place and then inexplicably get back up and win the day.
Facebook isn't what it was from my under twenty-five friends. Seems to be no longer particularly cool in any way, just a functional thing for organizing parties and letting people know when you're in town. I don't know how you displace that, but I don't think there's any great loyalty to Facebook. If Myspace offer something that is more convenient with less ads and hassle... Still seems unlikely, but maybe. If they offer good tools, perhaps.