Based on a couple of additional Google searches, my current guess is that Illegal Burger ("IB") is replacing a Smashburger. This link: https://www.scrapehero.com/location-reports/Smashburger-USA/ indicates that Smashburger had a unit in the Pepsi Center/Ball Arena in 2024 (search the page for "1000 Chopper Circle"). But this link: https://denver.opendi.us/12176862.html says that Smashburger is now closed. However, the Smashburger closing and new "IB" plans could be completely independent. Nevertheless, that job posting alone confirms, or at least indicates, that there are plans to open an "IB" in the Ball Arena.