Absolutely!!
the current pricing is insane and the supply is even worse.
Indeed, it would seem like the RF mount would be a real gold mine for Sigma to move into. Over the past 4 or 5 years Sony has allowed the price of many GM lenses to drift down a bit - you can usually find the 85GM and 24GM both for good prices while their 16-35GM and 24-70GM lenses are now quite reasonably priced.
Canon is of course probably wise from a business point of view still keeping the newer RF L lenses priced high as they are able to recoup some R&D costs and sell them to the pent up demand and GAS-afflicted though I imagine in the medium term Canon will lower prices - They won't want a situation where bread-and-butter professional lenses like their "holy trinity" 2.8 zooms or their fast 50 and 85 are so markedly more expensive than those from their main competitor.
So for the moment it would seem easy pickings for Sigma - they could undercut Canon pricing by several hundred dollars on many lenses and the modern Sigma standards in terms of optics, quality control and build is these days excellent, in many cases superior to Sony and second only to Canon itself. I would particularly like to try their unusual 45mm/2.8 and the 14-24/2.8 for astro due to its low vignette.
Maybe the problem is the issues around Canon not making the mount open? Given that it's wider than the Sony E-mount one would think physically it would be quite easy to port over their current E-mount lenses so perhaps it is the issue around the licensing, laws etc. I also am surprised that Voigtlander hasn't released any RF mount manual focus glass. Maybe negotiations are all going on behind closed doors and we all just have to keep guessing.