I've wondered about that too and it got me thinking, was the 70-300 a practice run for a DO zoom? However, given the price of the 400 DO f/4, what would you be prepared to pay for the 200-400 f/4 version Then, imagine a 200 f/2 to 400 f/4 zoom with the big front 100mm DO elements supporting both. That would be a fantastic lens and fantastic price. Perhaps they'd drop the price of the 400 when they released the zoom?
But in answer to your question, no, I've not heard any more