As the network grows it becomes increasingly harder to do so, especially since you need to add increasing amounts of resources (bandwidth, disk space, and some cpu, for the proof-of-resource) to your attack.
This is not too dissimilar to what happens with CPU-only PoW consensus networks. Easy to attack in the beginning but less so as the network grows.
It will be interesting to see how the SAFE network will be bootstrapped. I'm sure there will be a significant number of malicious players waiting in line to disrupt it early on.
If it works, and I believe it can, IMHO this network will be one of the most important developments in decentralised systems in the past decade.
Probably, and since untraceableblog.bit already points to his host's IP address, all that's needed is for him to configure that domain on the github side (and probably also untraceableblog.bit.pe for folks without .bit resolution).