I could be wrong, but I don't think they are renaming anything. They just replaced the official Node.js Github repo with the io.js repo, and it has the old readme. I expect the readme will be updated.
It seems like the future-facing work is being done in the io.js repository.. that doesn't mean an eventual release from there will be called io.js. Can anyone link to anything more authoritative than a probably-not-updated README?