Initially I thought the next step would be some sort of datalogger, but it has occured to me that 3-4 GoPro cameras could collect some interesting data. One camera looking aft from the towplane release area like in the following video...

https://youtu.be/-EbSg4YLrfQ

Then 2-3 cameras in the cockpit. One in a position to see the elevator inputs during the flight, one positioned such that the horizon is visible with perhaps some marks visible that could reference pitch angle.

Then perform a couple of kiting events at altitude and done in as safe a manner as possible to collect data. Unfortunately I’m not a towpilot nor do I own a towplane.