I’ve just tried to access OSM using an IPv6 only connection, just to see what happens. http://openstreetmap.org works, but no tiles will be loaded. This wiki here is inaccessible via IPv6. -- Sloyment (talk) 15:48, 22 February 2014 (UTC)
On a IPv6 only connection you should use DNS64/NAT64. From a real IPv6-only access the world is still very small.