And this isn't great for tourers at all... proprietary systems which a normal LBS doesnt carry are absolutely a nightmare for a tourer. The romantic idea of vacation riders in the bush fixing their own stuff is extremely rare.
I can understand that in the Netherlands its pretty rare to have to fix something yourself whilst out touring, but I live in Australia. Once I get out of my capital city, there's stuff all LBS until I hit the next capital city, of which the nearest one is about 700km away.
When I was touring in Africa on my recumbent we ran big HEAVY DT 340 rear hubs (after my XT M770 cacked it on the Nullabor Plain in Australia, 1200km from the nearest bike shop, and I had to get lifts from people and a bus to get back to the city to source replacements...), which were overbuilt with the heaviest rims and spokes and spoke count we could fit into that size. Because, if we had a failure, the best we could hope for was to somehow get transport a thousand km or so to the nearest decent capital city, then get parts posted in to us. This wouldn't have been any different if we were running a shimano/DT hub (unless we carried like 500g of spare parts and tools) on say a 26 inch wheel, as Africa just doesn't have parts for multigeared bikes much outside of South Africa. They are really hard if not impossible to get. You can only find single speed wheels, sometimes if you are lucky and in the right country and area, to get you out of trouble.
In that situation when I do something similar in the future, I'd much rather have something like the Kappius, which is much less likely to break down, builds a stronger wheel, that I can fix easier if it does (and clean easier, woohoo!). Because it really sucks to have to mess up a big trip that you've been planning and saving for ages for a mechanical failure, that can now only be solved by having to get days of odious transport and then wait for parts to arrive. Or have to carry a heap of extra weight in spares
As for "exceedingly rare", I give you that, and this isn't a replacement for the existing hubs out there for most people. But that's just like how there is just no need for a Lightweight Mielenstein for most people out there, or carbon fibre chainrings, or , drilling holes in your gear levers to save 3 grams isn't actually needed for most people. This is Weight Weenies, which is very small niche, just as is the niche that needs a hub like the Kappius.
Those in the niche, know who they are.
PS, one day I hope to tour in the Netherlands, it sounds awesome!