I'm not sure it will be much different from the current trade possibility of Canadian BTC ETF + CME BTC futures. IB will likely set the margin requirement for spot BTC at 100% and the short futures will have a varying margin requirement that tends to be raised at the worst moments. So the margin concerns in the trade should remain the same
While I suspect confirmation of a launch date isn't market sensitive info, I'll have to play it on the safe side and just say an announcement of an official launch date will be made in due course.