Hi @akash great to hear you are interested in joining GSoC!
I am sorry to say that I just heared the Media Repository is being implemented already for a client project so I think it would be best if you have a look at one of our other ideas at: Ideas — Plone: Enterprise Level CMS - Free and OpenSource - Community Driven - Secure. From that list I know one student who wants to work on the Workflow Manager. If you are interested in any of the other ideas let me know and I will gladly provide you with more information.