Note that this move is broader than just ICANN. IANA functions are actually run in close coordination with a number of organisations, for instance, regional internet registries (RIRs) and IETF who decide about address allocation policies and protocol number allocations.
Here are some initial reactions from all of these organisations:
IPv6-only networking does work, surprisingly well. But there are a number of issues as well, and some hard work will be needed to resolve them.
For one, we were early transitioning to this mode and hit many of the bugs in various operating systems and applications. The situation has improved dramatically in the two years since we turned on our IPv6-networking mode, for instance Linux today works much better than it did back then. Still, some bugs remain. And I think the users need to push some of the application vendors to make the updates. For instance, while there now are recent versions of WoW that support IPv6, the same is not true of most other games. Similarly, Skype has known about their lack of support for IPv6-only networking for at least two years. When are they going to publish an update?
You should try to IETF tools site, they have very good linking of the various RFCs and how they depend on each other. For instance, if you look at http://tools.ietf.org/html/rfc5395 you can click on the RFC it replaces (=obsoletes) or the RFCs it updates.
Q: How many IBM CPU's does it take to execute a job? A: Four; three to hold it down, and one to rip its head off.