Holy crap, thanks for sharing this. I'm still pretty new to macOS, but I absolutely love Voidtools Everything on Windows. If Cardinal supports the same syntax as Everything and is anywhere near responsive, that'll be a gamechanger for me.
Cardinal seems to be almost as responsive, except that the current search doesn't update when you delete a file that's in it - you have to search again for it to be gone. IIRC Everything auto-refreshes the view.