I mainly meant it as an example as to what could do to translate a banking system into something more interesting (also, a bank might not enslave you, but if you go to loan sharks to pay the bank, then maybe you can get involved into black market stuff, and so slavery). My point was that a banking system in a vacuum is not relevant or interesting. I don't really find immersiveness on its own a good enough reason to work on any system.
Actually, I am sure that I could have players fall prey of shark loans without a banking system (being robbed and/or scammed could leave you in debt, without me having to create a surrounding system, and without strictly forcing it on anyone). Regardless, the point of contention here is that the system was worth adding for immersiveness, which is something I fundamentally disagree with, and is against my design philosophy. Just like I don't have players eat, drink, go the bathroom, many of the things I don't add are abstracted away for the sake of the gameplay. Things that are added are usually meant to be interacted with in a meaningful way, to justify their existence. A weather system might be "immersive", but if it's going to mean nothing for the gamplay, you bet I won't add it in.
I can come up with many ways to make the system have interesting consequences or interact with the world at large (and I mentioned a few myself), but that doesn't have much to do with immersion, that's just content.