We're told that the next L lens from Canon will be a prime and it will be coming in late summer/early fall of this year. While the source wasn't sure what lens was coming for sure, they did let us know that prototypes for a replacement of the 35L were out there. This has been a long rumoured lens for replacement, with multiple patents for the optical formula throughout the years.
For the moment, lens production capacity is what will dictate when new lenses are announced. The brand new EF 100-400mm f/4.5-5.6L IS II has been out of stock around the globe at major retailers for a long while now, so I'm sure that has priority for Canon. As well as the brand new and highly touted EF 11-24mm f/4L.
The only other primes I've had multiple discussions about are replacements for the EF 200 f/2L IS and EF 800 f/5.6L IS. Just like the 35L however, those mentions have been around for years. Interestingly, there hasn't been talk of new TS-E lenses in a long time.
Outside of that, we're still waiting on a new non L 50mm lens as well as a non L/non DO 70-300 replacement.