It's interesting that when asked whether a 17 fold increase in licence fee was likely you rubbished the idea and yet didn't give any valid assessment of how much you thought the licence fee would go up by, even though the poster asked for your opinion.
The problem faced is that the canal system was renovated from decay and dereliction by others, starting with Tom Rolt, Robert Aickman and Charles Hadfield. It wasn't created as a business opportunity by either British Waterways or CRT since had the above three individuals not taken action there would now be no viable canals in the country. You seem to have the approach that CRT should be pursuing a business agenda to attract people onto the canals by giving them favourable terms whereas the agenda for CRT is to maximise income from whatever source to maintain a national asset. Your objection to an automatic income stream is not valid, how else can they make any plan for maintenance if they have no certainty of what their income will be. By relieving the vast majority of boat owners from any requirement for a licence except for the few weeks that most boat owners actually use the cut, the loss of income would rapidly lead to the demise of the canals (again!). I'm old enough to remember the derelict and trashed canals, are you?
Your hope for the DEFRA grant to be 'secured for the future' is precisely that, a hope, and one that is unlikely to be realised by a Government that is intent on cutting costs throughout its sphere of influence. The current Grant arrangements run until 2027 (another 11 years) and for a Government that isn't financing other far more important elements of society (Mental Health Care, Elderly Care, etc) I wouldn't hold out too much hope for the arrangement to continue. I couldn't see much chance of a successful case for the Grant being made by CRT if they had ditched a source of income such as the contractual requirement for marina boats to be licenced, why would any Government agree to bail them out when they have abandoned a guaranteed income source?
As has been repeatedly said in the past, if you don't wish to licence your boat in a marina, use one of the marinas that are exempt or alternatively use those who will store your boat on a hardstanding where a licence fee is not payable, as I have travelled around I see that idea becoming more popular.