Recall that we have almost a year before the new edition's PHB comes out.
Also, didn't he say that he was going to take an extended break (for health reasons) after the current story line wraps up?
So, I'm guessing that within a month or two the current story line finishes up, after which he takes a few months break, coming back almost in time for the first "Wizards Presents**" book. So, as the new storyline starts up, he will then convert the characters over based upon what is in that book - perhaps making adjustments later if the intel from those books turns out to be off a bit.
** (Although initially suspected to be books detailing how the 3.5e adjustments were made to the classes / races / monsters / etc and what was going through the developers' minds at the time, it now appears that these are to be previews of the upcoming 4e classes / races / etc, detailing what changes were made and why. They are due out literally months prior to the PHB, as I recall. In fact, I'm surprised there has not yet been a thread started about this! )