Yes!

If they did a 100% new optical design for the RF mount, with it's wide open 20mm flange distance, then you use the identical optical design with a mere 4mm extension of their barrel so it'd fit the Nikon Z mount with it's wide open 16mm flange distance. And the Leica L mount is exactly 20mm, so that the identical optical design can now be used for the L mount Alliance of Leica/Panasonic/Sigma. That's 1 new series of optical designs to fit 3 of the 4 main FF mirrorless mounts (excluding Sony FE which they're already heavily supporting). Come to think of it, wouldn't they just use their existing L-mount optical designs and add them (& new ones) to fill the RF lens selections? That would be the obvious thing.
I'm sure Sigma would be aware of this, and that's probably exactly their plan.
Come to think of it, I always wondered why Canon would choose a 20mm flange distance for their new RF mount when they could have used a shorter one (like Nikon did) to get even more options in lens design with lenses closer to their sensor. Now I think I may have the answer - Maybe they did it to match the L-mount so 20mm flange designs would work for the 3 major flange mounts! Wow.