From B&H Photo
B&H and Adorama have the new teleconverters in stock. I have one of each on order.
The Extender EF 1.4x III and Extender EF 2x III have been designed to complement the latest range of L-series lenses, matching their appearance and offering a visible differentiation from previous models. A carefully positioned lens release mechanism also makes it easy to mount the extenders quickly, reducing the time that the camera and lens are exposed to the environment. The extenders offer the exceptional build-quality expected from Canon’s professional products, and are resistant to both dust and water, allowing photographers to use them in extreme shooting conditions.
Canon seems to think so, I do expect performance improvements. Anything to speed up putting on and taking off the converters is very welcomed.