In this post I put up some plots with the posting and linking rates in our political Usenet data set. Would the political Usenet continue to decline at the current linear rate (according to the past 4 years, and using a rough linear regression in R), the post rate would approach 0 around July 2014. Here is the (unsmoothed) data for posting rates, and the completely unoptimized linear fit in R.
Of course, it's safe to say that regressing on 4 years of data and projecting it 6 years into the future will leave a huge margin of error-- even the fit "looks" like it should be a little steeper. (Smoothed data gives the endtimes to occur a year earlier, and I imagine more sophisticated time series analysis would project something completely different.) Errors involved in fitting aside, there's no telling what other sorts of things could happen between now and then to bring it back or (perhaps more likely) speed its decline.