I would very much doubt any of those carrier-grade routers run BGP in hardware. Chances are the control plane is handled by a bog-standard Linux/VxWorks/BSD tha

I would very much doubt any of those carrier-grade routers run BGP in hardware. Chances are the control plane is handled by a bog-standard Linux/VxWorks/BSD that does all the logic of talking BGP/etc and then populates the right registers in the switching/routing hardware which handles the actual data plane. You could technically replace all the control and decision-making with whatever off-the-shelf computer platform you want, and have it drive the carrier-grade router and "manually" populate its routing table via some API/Telnet/SNMP. In fact, as long as the hardware packet-routing core is still good, this might be a good way to upgrade out-of-support equipment that is no longer getting updates to its control-plane computer.