Brad from IBM/OpenBMC here. We make peripheral expansion cards that bring the pcie fabric out of the main system chassis via a cable. These cards have LEDs next to one or more connectors on the card. These LEDs are distinct from identification LEDs for the expansion card slot itself (we have those too - I think Gunnar has asked for this elsewhere).
My stab at modeling this within Redfish would be to implement Fabric (type PCIe), Endpoint and Port. What I think I'm missing is IndicatorLed on the Port object? Am I close?