Also,i'm sure you know this, but security through obscurity is a poor systems design choice in almost all scenarios.

The only time I can think of from the top of my head where obscurity aids security is when secret keys are kept obscure. This isn't even what people mean by "security through obscurity" though, so I'd actually beg someone to give an example where obscurity is actually beneficial to security and doesn't just give a false sense of security instead.

That's not to say everything can or should be open source, of course, just that relying on it being closed source for your application to be secure is a good way to open yourself up to attacks.