May be hard but the way the future is going probably something todo with streaming. It depends what you are going to compete against and knowledge, Like a site such as Facebook may be almost impossible to rival unless you have A Cert and loads of passion that's why I said 'Almost' because nothing is impossible
Facebook won't be the big Social Network forever same thing happened to my space.
So it really depends what you want to compete against like I said streaming features like A unique way of face chatting for example would be great.
I have also noticed HTML 5 is making it easier for people to achieve these goals as they now have A <audio element which allows Music playback, Not sure about video but I have heard they have one for video a swill.
Just my advice and help.
A membership where you pay a reasonable amount and be able to share music. Like better than what we currently have. I can link my friend a YouTube video but id rather someone be able to just have it to listen to for a while.