I don't think MySpace had a micro-blogging feature back in the day, so I think that'd be the first thing that I would add -- a micro-blogging feature for posting text, pics, and videos. Toss in some inspiration from SnapChat and make the posts disappear after a short period of time. Ditch the facebook model of 'friending' and use twitter's 'follow' model instead.

That's a fun question to think about what one would do with MySpace, but I think the whole 'social' space gets too much attention. It's like Peter Thiel says, the next Bill Gates isn't going to create an operating system, and the next Mark Zuckerberg isn't going to create a social network (even though this isn't totally true, just look at Evan Spiegal & Kevin Systrom).