We were told previously that the next L lens would be a prime, and it looks like it'll be the EF 35mm f/1.4L II. We expect it to be announced on August 14, 2015 if the announcement date rumors are true.
Now we're told the next L lens will be a fast zoom (most likely f/2.8), but not until early 2016. An EF 16-35mm f/2.8L II replacement is the odds on favourite at present. Prototypes of an EF 24-70mm f/2.8L IS exist, but whether or not it will become a product anytime soon is anyones guess.
While the source was confident that's what we'd see, they did say it was possible a development announcement for a new supertelephoto could be on the horizon. While there's lots going on in development of a new long focal length lens, there is nothing imminent.
More to come…