Fully accessible, incidentally, would be wheelchair-width aisles - something which the UK loading gauge doesn't permit (except perhaps for metro stock, which isn't suitable for other operations).
But with that you fall into the trap again (not to mention that you can't, other than by using 2+1 seating in Standard and 1+1 in First, or very narrow seats, get that into UIC gauge either - it isn't much wider than the UK, maybe 10-20cm, it's just higher and squarer). A wheelchair width aisle doesn't have something to easily hold onto on both sides for someone who is not steady on their feet. Yet that person has to move through the coach to find a seat, the wheelchair user doesn't as their place is there for them.
Accessible areas in every coach is a decent middle ground that we can probably manage.
But is it necessary? All trains have at least one wheelchair space; rarely is it filled with anything other than luggage and bicycles. This could be because the processes need improving, or it could simply be that most wheelchair users prefer to travel by car, and indeed with Motability schemes are assisted to do so. If I became wheelchair bound and still able to drive an adapted car, I would certainly give up drinking alcohol and would drive everywhere - it'd simply be easier. Those people have enough challenges and there is no good reason to discourage them from driving. So you are left with a need for a residual provision for those who cannot drive or those who specifically enjoy rail travel.
I think I've seen two wheelchairs on a train once. Until then, 11 wheelchair spaces on a Pendolino would be an utter waste of space, and would mean fewer seats for those who need those, and fewer toilets for those needing urgent access to those.
It would be a negative development unless something significant changed. If most times I used a train I saw a wheelchair user on it, I'd agree with you, but I don't. Not even 1% of the times I use a train do I see a wheelchair user on it.
As for the loos, the TOCs are performance-managed on timekeeping, and in the peak, coaches provided in service. I think they should be managed on working facilities - accessible loos are very much not a deal-breaker when it comes to sending trains out, which is absolutely not right.
Agreed. A start might be to consider that the train is not wheelchair accessible unless the wheelchair toilet is functional, and to penalise accordingly. No toilets at all would give a higher penalty. But care would be needed to ensure they are properly motivated to fix the problem, not just cancel the train. (Though I think it should be mandatory, if a train runs without toilet facilities, for Advance and Off Peak restrictions to be lifted if a passenger does not wish to use that train, and this should be without them having to ask as this may be highly embarrassing).