I see the 24 70 4 IS and the 16 35 4 IS as better options for the 24 105 & 17 40 users without killing 2 wildly popular high selling basic L lenses in the 24 105 & 17 40.
They have not had opportunity to tackle faster 2.8 & wider lenses without jamming the market with all of them at once.
Makes sense for them to wait until Sigma is done with their releases. Canon with the 35 & 50 mark II has a real opportunity to totally deflate Sigmas recent ascention which is based partly on nothing else new out there (OTIS is a higher realm of quality)
Let me clarify; Sigmas lenses are great, but real world comparisons don't show them to be cadillacs to kias that a few loud and wildly optimistic individuals are claiming
There is much more to Sigma's recent success in the quality of their products than in their go-to-market timing. Sigma is doing well because it is putting out some fine lenses for terrific prices. And on the data side of things, specifically in resolution, Sigma is handily beating Canon, not just keeping up. The 35 and 50 Art are the sharpest AF lenses in their respective focal lengths, and by a comfortable margin.
I haven't shot either of the Sigma Art primes, but many trusted reviewers hold both of those lenses in very high regard. But a lens is more than how sharp it is. So I could see 'real world' reviews possibly not seeing as large a gap between Canon and Sigma in these focal lengths.
Canon must be working on some next generation L-series standard primes (24/35/50/85) that are intended for very large MP sensors. I think we are all waiting for those.