<<< Servers at MIT if I recall correctly. If these servers are inaccessible, what is the effect? >>>
Precisely, that is the problem.
<<< Perhaps "bootstrapping" is simply a matter of voluntarily downloading a trusted file, containing some reachable IP addresses. >>>
Could be a solution. The issue is again, from where we download it? If we download it from a centralized source then the decentralization does not exists. There are suggestions to solve this with Bitmessage or Telehash, but those are both having this very issue with bootstrapping. Using Bitmessage or Telehash for bootstrapping an another network is just kicking the can down the road. I understand you didn't suggest this :-) I am just saying.
The problem with DNS is that an authority can ban a domain name and the idea of permissionless systems is that there is no central authority should control the access of users.
mDNS and UDP multicast work fine on local networks and we are working to solve this on global networks as well. IPv6 anycast looks promising but I haven't got yet the prototype.