Don't wanna be killjoy, but specifically since "sleek" and "native" is mentioned many times, I'd say that's not what one expects from a sleek macOS application to say the least.
I'd expect something like Cyberduck quality UI, as an example. The author should aim to mimic system UI in my opinion as closely as possible (or integrate inside Finder).
I'd expect something like Cyberduck quality UI, as an example. The author should aim to mimic system UI in my opinion as closely as possible (or integrate inside Finder).