I don't think there are any plans to extend TRIWV to craft under 20m. When they came into being people were wetting their knickers over them, but the reality is that by and large they are sensible standards for a craft cruising continental watereways. The people most threatened are those who have little prior boating experience and who have perhaps bought a pretty little tjalk on their retirement which has served as a houseboat for many years and had all its bulkheads removed, its wiring a tangled mess of bodged handiwork, engine and fuel tanks a serious fire hazard - I could go on. I don't believe in over-regulation but it is difficult to argue against some minimal safety standards. Simplistically the UK BSS is concerned with the safety of the person in his boat, whereas the TRIWV is more concerned with making sure a vessel is a safe navigable entity - that the hull, engine, pumps, VHF etc are adequate for their purpose and in good working order. Groups such as the DBA have managed to get pleasurecraft exempted from most of the really stringent rules applicable to commercial vessels, though some do remain and are still under discussion.
Jim wrote extensively about his continental cruising for the NBOC if I recall, and although he starts out saying how great it is and how much narrow boat owners would enjoy the experience, he does then go on to detail pretty well all the potential hazards that I list myself. He is also extremely well-travelled in his boat over a great many years, which is a very different matter to several postings on the topic I've seen on here.
It is of note too that Falcon is held in the lock just loosely with the line in his hand - certainly not a technique you can use on the larger commercial waterways, and even the smaller Freycinet locks often fill at such a speed you would lose control of the boat if you did not take a turn with the line.