As somebody who owns four 550EX flashes used as slaves to a 580EX2, I very much hope that Canon introduces a small and cheap interface module that can be attached to the foot of a slave and allow it to be used with a new flash system.
Also, there is a "low energy" version of Bluetooth that seems custom designed for this application: low power requirements, fairly low data rates and low latency.
The idea of a radio receiver for existing flash units would make sense for most of us who have existing E-TTL2 Speedlites. I just fear that it may not make sense for Canon, who would like to sell us new Speedlites!
Given the cost of Pocketwizards, there is little commercial incentive for Canon to build a receiver for existing Speedlite users.