What you call "social coding" is simply the convenience of contributing to a huge number of projects without needing a separate account or quasi-account (joining a mailing list, using OAuth/OpenID, etc.) for each. It is not necessary, it predates and doesn't need GitHub (as Sourceforge demonstrated 20 years ago), and it will simply move to other project hosting communities, with a modest decrease of convenience in the transition between one account and a few accounts.