I found many existing and old editors (e.g. Notepad++, Geany, Crimson editor) do column selection with these shortcuts:
Alt-Shift-Down - like Shift-Down to extend/shrink cursor selection, but in rectangular column selection mode. E.g. try Alt-Shift-Down, then Alt-Shift-Right.
Alt-Shift-Up - like Shift-Up, but in rectangular mode.
Alt-Shift-Left - like above
Alt-Shift-Right - like above
Alt + mouse drag - to make a rectangular selection
However, in Atom, the shortcut is different (Ctrl-Shift-Down, Ctrl-Shift-Up) and with different behavior. I would like to point out that this seems a new invention and doesn’t maintain harmony with old editors.
Since Atom is newer editor with some potential, I would like to see its common features behave like the mainstream, but not unnecessary new invention.