Are you sure Sumit is the last one now? I think Mensik is still qualified right now, behind Sumit. I think Australia has only 3 qualified players (DeMinaur, Thompson, Popyrin). O'Connell has not been in Davis Cup teams. I think there is one extra spot available over the list we have here, and it goes to Mensik, right behind Sumit.
Can you confirm? I don't see O'Connell in the Australia teams at DavisCup.Org.