Whilst not directly related to TTN, there are possibilities for the SX1280 when you appreciate that (in the UK at least) there are no duty cycle limits if you use this 2.4Ghz device at 10mW, so it ought to be capable of moving a lot of data around.
I have it working now under my own Arduino library, and here is a report on some link tests, mainly on the ranging capability, but it does contain some details on the capabilities of the SX1280 for long distance links;
A summary here;
Summary - Semtech SX1280 2.4ghz LoRa Ranging Tranceivers
More detail here;
Semtech SX1280 2.4ghz LoRa Ranging Tranceivers
And some tests on the fast LoRa here;