I recently spoke with our FedEx account representative last week and they introduced us to FedEx Ground Economy, which was formerly FedEx SmartPost (link to information here: https://www.fedex.com/en-us/shipping/ground/economy.html).
Our contract now includes Ground Economy, but after calling into ShipStation customer support I found out it is currently not an option to select this or have it enabled. It would be a tremendous benefit to utilize this for our online marketplaces, and I would love to see this implemented on ShipStation and begin using this shipment option as soon as possible!