Du such emulators exist? This would need to be some special hardware. A normal IDE controller would not do it. IDE is hirarchical. There is one controller and two devices. A controller cannot be (mis)used as a device on another controller. One would need to put an IDE connector and the device firmware on a PCI card. Would probably be very expensive because it's not often demanded.
You can do this with SCSI. SCSI allows multiple host adapters on one bus. This can be used for networking or device sharing.
