Take this sentiment and jump forward 100 years. What's left?

I suspect this will happen to any namespace after long enough. Domain names, Twitter handles, Facebook URLs, whatever. Once enough real estate is taken up with immobile monuments to the dead, the living will have to move on to something else.

I also think this will happen well before 100% utilization. After some point, the number of collisions you hit when trying to get a memorable name becomes too much of a burden and you just go somewhere else, as previously described here: http://rachelbythebay.com/w/2012/11/28/namespace/