I would imagine Canon sell as many 24 to something and 70 to something L lenses as all their other L lenses put together, so I can see them having mileage in fleshing out those ranges just like they did with the EF range. However, as
@Maximilian says, it will be very big, heavy and expensive, but there are plenty of people who will see their images as being much better from a £4000 lens
I remember here on CR the ridicule and derision when the EF 24-70 f/4 IS was introduced, but that lens does offer a smaller, lighter and better balanced package than its contemporaries, with very good resolution across the frame at f/8 or 11, (and 5.6 at shorter focal lengths) matching all but the most expensive primes, and so a good all weather landscape lens.