Ugh...yeah, it does look like it was dropped from the command-line argument list for the force:org:list command in a very recent CLI update. I just reached out to someone on the CLI team at Salesforce as I wouldn't expect such a breaking change in what is effectively the public interface of a CLI command. Even if it's no longer needed, I would think it would still be accepted and perhaps logged as unused.
Let me see what they say before I make any changes, though, because if the removal was an oversight and it's going to be restored in a very short period of time, I'd prefer not to remove and then restore it.
Thanks for bringing this to my attention,