On reflection - you're absolutely right. In fact this is exactly the way OpenGB is designed!

OpenGB uses an abstract base class (called IPrinter) to describe a printer interface. At the moment there exists a Marlin implementation and a Dummy implementation (as you describe) of IPrinter.

Other comments mention BeagleG and MachineKit. It should be pretty trivial to add IPrinter implementations of both of these.

Thanks for the inspiration! :)