Slower versions of Canon’s well-regarded RF 28-70 f/2 zoom lens have been designed, and a patent application filed. The two primary variants both start off at f/2.8, with one keeping that up through the zoom range to about 70mm; and the other necking down to an f/5.6 by the time it reaches a zoom range of about 90mm.
As Canon already has two versions of the 24-70mm zoom range – and f/2.8 and an f/4 model – the embodiment most likely to be of interest here is the variable aperture one that extends to 90mm.