Dissertations / PhD on Social Networking Websites / Marketing / strategic Management - topics [10]

I am planning to do PhD in marketing. I am very keen on Social media marketing with special reference to Facebook. My apprehension is these websites can become obsolete anytime. How long will my research be valid in such case? Or should I do some modifications to be able to stick with this area?

I personally believe social media is here to stay. But you never know with the technology?

Kindly guide me on this.

Regards