The decentralised nature of this system will directly threaten Facebook, Twitter et al.
The DNS system works, and scales, because everyone publishing information to the DNS is responsible for the upkeep of the nodes that publish their own records.
Facebook and Twitter, however, have scaling and financial problems. Facebook, so far as I am aware, continues to make a substantial annual loss despite its enormous success, and I have yet to hear that Twitter has managed to turn a profit.
More importantly, the privacy of everyone publishing much of their personal, private correspondence using a small number of centralized agencies is directly threatened -- and it could get particularly messy if, in a few years time, $SOCIALNETWORK fails to become profitable, goes into receivership, and the vast databases of private information are identified by the administrators as the organisation's most valuable asset.
In contrast, a Wave infrastructure, like DNS, will distribute the upkeep and storage of private information to many (hopefully) locally trustworthy systems. Because of social engineering / hacking attacks, leakage of private information can and will still occur, but the impact should hopefully be minimized if the Wave protocol and its implementations have been suitably well engineered.
This is going to be interesting.