I think your cleat on the bar idea is brilliant. I think it would work well one handed also, since you would have one hand on the center bar, sheeted way out, a slight pull on the center lines with that bar hand, and there would be almost no pressure on the line at the cleat to resist you.
I kited with the 17meter Cloud C2 and the Paipo (quite a light wind set up) in this today:
Kind of a 5 to 18 mph range I guess. I flew the kite higher during the higher winds for sure, but never came close to needing to fully extend my arms. The bar position moved of course....but never felt too far out or too far in. And this, too a substantial degree, is due exactly to what you said...the great change in kite behavior with a lesser amount of bar movement for the Clouds.
I like flying the Clouds so much that I didn't really want to go back to my other kites again to test. Hoping others would. But I will look for some wind that is really a bit too high for my 13.5 RRD and give it a go. What I can say is, in regular conditions with that kite and the BRM CS, the canopy flattened between the struts and the rear lines went slack well before I reached full extension. That is to say, I think it would work fine for your walk. I think, not I know. More testing needed to be sure.
If one has quite short arms and a waist harness that has ridden up 6 inches...maybe that could be a challenge (as it can also with a bar that loses range of motion when trimmed way in). Because I can get the Cloud kites to depower both more fully and more immediately than my others....my waist harness riding up is much less of a concern...ie. not a concern. A gust I feel mostly in the bar....the bar goes right out...and I get no harness tug.
You know...continuing the slight aside conversation...Cloud/ CS riders are thinking drift, fast, and stuff like that. The person I want to give a 9m Cloud with a CS bar set on the closest knot and with a well secured seat harness is that kiter we have all seen: The 105 pound 5'2" woman who launches a kite and is flying down the sand overpowered and struggling to pull a trim strap and even after pulled in is struggling due to her limited reach. Giving an extra 5 inches of throw to that person....plus a kite that will depower more than any other with that extra 5 inches out...seems like a safer proposition to me. Just a thought.
I was quoting Slappysan in regards to the walk etc., but I have occasionally had a 400m walk to the water's edge from where I launch.
The cleat as shown is 1:1.
I don't think it is going to be practical to do it one-handed unless there is very little power from the kite.
I think we will just have to wait and see what people's experience is of using the BRM bar with other kites to see if trim-on-the-fly is preferred to trim through sheeting range. I guess it also requires using it for long enough so that it becomes 'which is better' instead of 'which am I used to'.
It could depend on the geometry of the kiter as well as the kite - as you suggested.
My other kites flag to two front lines, so the BRM bar unfortunately would not suit them.