We could get another fork come Oct-2012 if 51% of miners are not using the new -qt client. That should be plenty of time.
This will never happen as you won't be able to get the majority of hash power to convert. Luke-jr (afaik) controls 600 Ghash or so of the chain and I doubt he'd update.
If he controlled 51% of the mining he could have killed off I0coin months ago. He wouldn't have to wait for a new client.