It looks a lot like the command palette of sublime, vs code, etc (cmd+shift+p). Combined with the navigate functionality of those editors (cmd+p). Where actions like back map to the command pallet and navigation like .articles maps to the file navigation.
Exactly. "Command palette" is the name of this user interface element known from many editors, app launchers and OS app integrations and is proven to be extremely efficient. It almost seems like the article is reinventing it and calling it "command line".
BTW even in VS Code there is in fact single unified input: "Go to File input" (Ctrl+P) that changes behavior according prefixes; "Show all Commands"(Ctrl+Shift+P) just opens the same input with ">" prefilled; "Go to Symbol in Workspace" (Ctrl+T) prefills "#", "Go to Line" (Ctrl+G) prefills ":" and so on. It even shows you placeholder when empty that reads "Type '?' here to get help [...]" what lists all those prefixes.
