These are good points, Chris and I don't doubt your experience. Damping and mass of the wheel itself are certainly factors to consider. However, every single time I have encountered tail wheel shimmy on my plane and others, it was directly caused by (and solved by) adjusting the caster angle of the pivot axis. My plane was shimmying badly during my trip out west. The steel spring had sagged and was making for a negative caster angle. On that trip I purchased a used Grove aluminum spring. After installing the spring, all shimmy went away and as you can see, it has a positive caster angle. During the spring installation I disassembled the entire assembly to check for wear and anything else I could find. All was good and the swivel action is very free and loose. The chains also have some slack in them. No shimmy at all.
I would think the number of fold, unfolding cycles would have to be astronomical for there to be a problem. Like the elevator horn bolt on an Avid, this might be something to be inspected every so often if you fold on a regular basis.
I have that system shown in the box, installed on my plane now. I hope it lasts. My next step will be to replace the slip/sleeve joints on the muffler with proper ball and socket joints to allow for some movement. I believe this is the major problem area. It is where my first plane cracked (as well as around the stinger) and where my last system on the plane cracked prior to the stinger failure. If you look at the cracked muffler you can see the major reinforcement pieces around the slip joints. This misaligned the sleeves enough that assembling the system went from a real pain to almost impossible. IMO, this exhaust system is a poor design from Kitfox with many area that could be improved.
If you look closely at the video, you can see the plane was in a stall with the yoke all the way back when it hit the runway. The failure to fly the plane was as soon as power was being lost the pilot did not push the nose down. MAYBE then, there would have been enough energy to flair, maybe.
For me, I wanted "notches" of flaps instead of the infinitely adjustable system that came from the factory. A personal preference. I further modified my plane with an elevator trim tab to eliminate trimming with the flapperons.
No photos. I'll take it with a grain of salt. The Mangy Fox had an advertised empty weight of 575#. There was that much dirt in the damn thing! With the BRS and all the other BS in it, it wasn't even close to that. Now she's a portly, but happy 702# empty. I have a good friend who built his Kitfox IV-1050 very, very light and was conscious of every ounce. He started with a 582 near the 500# mark and after he converted to a 912UL his empty weight was 585#. Maybe it can be done lighter than that, but I haven't seen it personally.
Moving the seat will be near impossible. Extending and lowering the footwell is a far better option. This "C" model Avid fuselage belongs to a friend of mine who did the stretch and lowered and stretched the footwell like you want to do.
What ever you do, be sure to factor in the 300 pounds that engine will weigh. Your gross will still only be 950 (?) that the "C" model airframe was designed to...