Pipes? Dbus? Goldfish? Why not use binder for everything? Both in-system and guest-to-host?
Seriously, binder is a very good IPC system and is required anyway for Anbox. By definition.
In Android O the binder is used even more extensively - as the base for the vendor API. Even if Android O support is still a distant goal, you can start with backporting the latest binder. It improves performance and adds new features like multiple instances.