Nobody wants to do this, though, as it would destroy the fabric of the internet as we know it or something. But a simpler method would just incur more government push back in an arms race around censorship. Do what the chinese [citizens] do: go covert.
But outside of which country? You'd have to read the local news for every country in the world that currently has them, every day, if not hourly.
What happens if people start selectively paying attention to the ICANN root servers? For instance, my computer is set to use google's DNS. What happens if the DNS admins at google decide that they're going to just ignore the update from ICANN?
And what happens if there is a second-tier DNS that crops up specifically to thwart attempts at messing around with the records? (Honestly, domains being 'seized' should be treated like faulty equipment. If a drive starts bailing out, you replace it. To me, it sounds like the US gov't's ability to modify the DNS at their will is a click-of-death on the DNS)
[1] http://dot-p2p.org/ [2] http://en.wikipedia.org/wiki/AlterNIC
Potential legal issues aside, what you end up with is a New Internet. Of course routes all remain the same, but nobody refers to addresses or routes: they use host names. Thus you run a huge risk of networked applications just not working, which would affect everything from entertainment to commerce to government services and god knows what else (what if medical devices in hospitals needed to retrieve a firmware upgrade and couldn't connect to the right host?).
In practice there would be no technical hurdle to do this. It's simple to just configure your domain name server to include some records, leave out some records and change others. Some people do this if their ISP redirects failed lookups to some advertising-laden homepage, for example. But on a large scale, the modification of the naming system to one's personal tastes has broad-reaching negative consequences related to availability of hosts and the functional and legal consequences therein. On a personal scale (modifying only your own name server results), you get to connect to your poker site again. I prefer the latter solution. If operating systems just started including a simple GUI to modify their personal domain name caches we probably wouldn't need an alternate dns root.
I think, however, the domain seizures just emphasize the importance of using a system that doesn't depend on regularly constituted DNS and getting more and more P2P infrastructure in place. I2P should be looked at as particularly promising.
You could harvest IP addresses from the IRC channel, but you could also do that by running the client and noting down which peers you connect to. Unless you're running behind Tor or I2P, it's not hard to figure out which IP addresses have connected.
However, assuming the government had this list, what would it do? It's hard to bring charges against a large number of individuals scattered throughout different jurisdictions, and historically, the US government hasn't gone after the people using alternative currencies; they'd go after the source.
They could shut down the Bitcoin site - which would be quickly moved to an international domain. They could try and prosecute the lead programmers of the Bitcoin software, but this would not be particularly successful. It wouldn't stop Bitcoin, and I think it would be hard for them to show the currency as being illegal without, for instance, affecting MMO currencies as well.
I figure their best move would be to shut down the currency exchanges, or at least tie them up in court long enough to damage confidence in the Bitcoin economy. However, if the exchanges win, then Bitcoin has an official seal of legality, and a huge heaping of press attention.
Probably original bitcoin author remained anonymous for the fear of government's retaliation.
And there are about 300 hardcoded nodes right now from different countries.
I think hardcoded nodes are updated only manually via git.
http://kotaku.com/#!5515459/south-korea-to-impose-overnight-...
As for Bitcoin, you can research the legal history of various "digital currencies" and you will see that there have already been problems in this area. The purpose of Bitcoin, a decentralized and unregulated anonymous medium of exchange is obviously contradictory to the government's aims. It all boils down to the fact that governments want a monopoly on currencies and want to be able to monitor and tax economic activity. Digital economies are growing rapidly in size and social importance and they are no more likely to be allowed to flourish unregulated than the free sharing of copyrighted media was.
Your reference to Bitcoin is apt, as the government siezed $7M in gold, silver and platinum from a political organization who was advocating the use of generic silver and gold rounds instead of depreciating paper currency.... and just a few weeks ago succeeded in railroading the leader of that organization.