Did a comparison of the RF 15-35 f/2.8 versus these new lens designs. They're about identical. This suggests that there would have to be two things to make that design work: IS and the UD elements required for the f/2.8 design. Implications: it will be spendy. The 16-35 version of the new patent is significantly smaller than the 15-35 version.
Interesting that widening to 15mm instead of 16mm makes the lens 16mm longer. I've shot a lot of EF14mm/2.8 and love a wide view. In principle I'd love a 14-35/4. But is it going to be massively bigger than a 16-35/4 could have been?