Canon recently announced the EF 400mm f/2.8L IS III and EF 600mm f/4L IS III on September 5, 2018. The new super telephoto lenses received a weight reduction of about 25% and 20% respectively.
Since the EF 300mm f/2.8L IS II and EF 500mm f/4L IS II should be announced by mid 2019. Do not expect the same level of weight reduction, as those two lenses are significantly lighter than their 400mm and 600mm counterparts to begin with. I expect a weight reduction of about 1/3 to a little more than 2/3 of a pound, respectively.
The one lens I am most interested to purchase is the EF 600mm f/4 DO BR. Canon showcased it during the Canon Expo in September of 2015 in New York City. This will be the ideal Super Telephoto lens for wildlife photography for me. My current EF 400mm f/4 DO IS II can be a bit short on occasion.