Short lines rule.

Just from the point of view of a more relaxing/enjoyable/safer super high wind session they rule.

6m lines can be hard work when it is gusty but they keep you fit. Been riding an old 4.5m arx on 6m lines for years when it hits the upper 30s to 40s. There is very little chance of teh kite looping accidently cos even with micro kite swoops teh kite tips are hitting the water.

Short lines are great, it's really direct feeling, it reduces the latency in response of the kite, which is great when timing a boost on a ramp, or if you need to correct the kite position instantly.
I love my GK Trix 7 and 9m on 16m. I prefer the 12 in 20m though.
However, there's a point where you hit diminishing returns. At some point (below 13m maybe), there's just no room for the kite to be downlooped, unless you bring it at 12 o'clock before looping, which defeats the purpose. Specially when waveriding, there are times when you need to turn your kite quickly one way or the other. Restricting your options in that regard is not the best option!

As for using less space on the water with short lines, I'm not really convinced. With short lines, you have a smaller flying window, but therefore you have to use pretty much all of it. The kite has to be spot on in the right place. Put it a few degrees higher and it's out of the power zone, lower, and it's in the water... So when passing or crossing someone, you can't really move your kite out of the way and carry on riding seamlessly until you're clear from the other rider.

From the vid it looks like you like to be very powered up on shorter lines. I prefer being slightly under powered on small kites and a surfboard. (20+ knots on a 18-20 meter lined 5m C with a 6'4 surfboard are the conditions that make me smile.)

I wish I could go shorter than 18m as I love the direct feel and added speed of the kite, but the power stroke on tiny C kites is just too weak. I've found I can't go shorter than 18m on my setups.

Looks like fun tho. If I owned a TT and a kite bigger than 7m I might try it.