That menu is where WinXP-style shell extension columns go. They aren't currently supported in collections but it might be possible for us to make them work in the future.
There aren't many people developing them these days, though, since they don't work in File Explorer from Windows Vista on. They're only of use to people using tools like Opus (or old, unsupported versions of Windows).
Thanks for the prompt reply Leo.
So far I have tried Opus, TC, and xplorer2 and I really like the interface of Opus - however, the inability to add the custom column in the search results is a deal breaker as I need it in my workflow with TortoiseSVN and Windows Search.