At the CRT Navigation meeting, which I attended on our behalf., a general comment that they would seek to limit wide beam boats from accessing waterways which were not really capable of allowing the navigation of wide beams was made. It was illustrated as I recall by comments about moored wide beams not allowing navigating wide beams access to the channel, and reference to air draught problems. This was verbally presented as a local matter, not for example affecting transit on main line waterways like the Grand Union.
Reading between the lines they may also be seeking to stop people craning residential wide beams into narrow canals, which would present them with costly removal issues if dues were not paid, and would change the character of those waterways, if allowed to proliferate. So I expect a list of short sections of canals built as wide and possibly all narrow canals to be forthcoming, but until they put some flesh on the bones of their general intention, there is nothing we can respond to.