It's important to point out though that even if the root servers were disabled in anyway, DNS is designed in such a way that we could easily create new ones. In fact one of the ways that Turkey suppressed twitter was by modifying the routes to some of the popular root dns servers. If you _really_ wanted your own custom tld accessible from the world, you'd just have to a. Run a server which would field requests for the tld
b. convince admins to direct queries to your server a. is easy you can do it with modern nameserver software (TOR does this with .onion addresses in fact)
b. Is going to be harder. Why should admins trust you? How do we know that you aren't going to rewrite other authoritative addresses for personal gain? There is a historical reason for all of this though, and it takes us back to the mysterious year of 1998! Jon Postel emailed the admins of several DNS root zones and subsequently changed Network Solution's primary ip address. It pissed of the military brass who thought they were in control and they threw around a memo talking about how they needed to improve the nature of how how internet names and addresses are managed. In other words, Postel at that moment in time literally had the ability to control the entire internet. He could have easily used it for profit, he could have sabotaged it. He could have made everyone's computer give him $1. When the government realized this, it hurt their feelings and pride and they took away the power. If you'd like to know a little more "inside baseball" stuff about this, you can read this RFC which was made to commemerate Postel: http://tools.ietf.org/html/rfc2468
You've outlined it really well — the DNS system seems to be series of servers that we've all agreed to trust. It would be easy enough to set up your own servers and direct popular domains to the wrong place or have a gateway to some alternate Internet. I don't know how those much talked about "darknets" work, but I know enough to imagine some techniques they might use. The idea of there being a secret second Internet makes me feel like a kid looking for a secret passage behind the bookcase, but alas if there really is a secret Internet then it's probably very seedy. And thanks for the Jon Postel story! I love these "man behind the curtain" kinds of Internet yarns. Vint Cerf's memorial for Postel was very entertaining and moving at the same time.
When IPV6 becomes widespread I predict we're going to happen to see a lot of new "private network" spaces which will be large, wide spread networks which use the public ipv6 space, but which use acls to allow specific networks to access them. We do this a bit now with NAT, but ipv6 could do this on huge scales and still not exhaust the available ips.The idea of there being a secret second Internet makes me feel like a kid looking for a secret passage behind the bookcase, but alas if there really is a secret Internet then it's probably very seedy.