Who would be able to implement the HoTT Telemetry into Ardupilot?
Support about the protocoll can be given.
Also a betaflight tree is maybe very helpful, these already mirror the OSD menu into the text telemetry display and allow PID settings and so on by telemetry.
Already tried and failed.
HoTT is pretty time critical and expects rather large packets at once when asking for them.
Mardhacker.org 's solution (with dedicated microcontroller) is the way to go unless Graupner make the protocol less time critical , and expect smaller packets. (Not very likely)
Why don’t using a DMA? The data can be send without the delays between the bytes, now or synchronise it with the 1kHz gyro loop time. 1ms per byte is now possible for sure. Sending one byte every 1ms should be not the big problem. And the answer for the telemetry request has a tolerance of 5-8 ms.
I believe that not only having a ArduPilot->HoTT would be useful but also getting the telemetry data from the Graupner sensors to ArduPilot would be a huge advantage.
Should be possible on the same UART TX halfdublex line.
If we are going to load up the Ardupilot code with Graupner Telemetry then I would like to put my hand up for JETI Telemetry as well.
We are just moving away from Graupner to JETI for a number of reasons not pertinent to go into here.
For telemetry we used the Mav2HOTT code running on an Arduino with good effect.
So we just switched over to the same boards running Mac2Duplex, also with good effect.
Since the boards are <$3 I am wondering what advantage having this code added to Ardupilot is going to have?
Larger builds have pretty much every input to the controller filled, so adding more sensor inputs is not going to work.
Nowhere to plug them into.
So maybe some expansion of the Mav2… Arduino code to allow the small cheap boards to take sensor data as well as Mavlink might be a better way to go.
I know the sole developer could use some help in expanding the work he started.
I am just throwing this into the pot as I am always wary of good programs (Ardupilot) suffering from bloatware through user requests and compliant programmers.
My 2C’s worth. 
I don’t like this additional boards at all, even if they cost only 3$.
HoTT Telemetry would also allow you to set all Parameters by the radio really easy, without the need of a PC. If the flash size is really a problem, then maybe it could be done by build option instead of the other telemetry protocolls, which will be not needed in this case.
Where can i get the full documentation of that protocol including this “DMA” mode ???
Please contact me by mail to get the protocol data.