So in Regis-de-giens video the kite is attached to a person. If the kite were to end up deep in the window and suddenly powered the load on the lines would be limited by how fast the kite flier accelerates out of the boat. Worst case scenario is a skilled kiter in the water body dragging back to the boat.
Long ago when I was learning to fly traction kites I attached a 12.5M Flysurfer Psycho to the roof rack of my car. It was a windy day and I didn't feel confident to launch the kite and hold it myself but really wanted to fly. The kite dragged my car about 50 feet then ripped the roof rack off my car.
I think you are doing the right thing by starting small e.g. with the trainer and a rowboat. Next might be a kitesurfing kite attached to a kiter in the rowboat as shown by Regis-de-giens video. I have seen similar video using a Hobie-Cat. You might try a kitesurfing kite attached to a kiter standing on the deck of your yacht?
You might check out Peter Lynn on the Max/Min problems and also Dave Culp Speed Sailing
Kites have come a long way since then, but we still are not seeing a lot of kite boats. As I see it the challenges requiring significant development are:
1) get enough sail area,
2) have a very simple drop the bar/control line depower system
3) have a weak link/fuse so if too much line tension is generated it breaks in a controlled and safe way, bringing the kites down on a safety line
4) have a traveller to adjust COE fore and aft, starboard and port
I think a Flysurfer Peak 4 would be a fun and interesting kite to play with for these purposes and at minimum would offer a nice experiment attached to a kiter sitting in a row boat.