@gandalf Application is not the right layer that should address this. In fact, it's not even possible with open system like thirtybees. We could fix all places in core that touches filesystem and change it to use this filesystem abstraction layer, but what about third party modules? Any module can use php filesystem functions directly, so this abstraction would be bypassed anyway. You would end up much worse -- some assets would be correctly synchronized, while others would not. And there's nothing thirtybees can do here -- we can't just force module developers to use our filesystem abstraction.
If you want to sync files, you need to do that on different / lower level. Either at php server (php module that tweaks filesystem api), or at OS level (map thirtybees installation over distributed virtual volumes).