Yes, I remember this thread about it.
Apparently LBT requires an additional FPGA not available in most gateways (although I think the Kerlink has it, maybe @kersing knows?), and only the RN2903 with the latest (beta?) firmware supports it as a node.
Mind you that the TTN network server (or any other LoRaWAN NS) might still enforce a fair use duty cycle (0.1% in TTN).