Blimey as far as I can see there is no suggestion that large twin engined boats are going to be banned from the Broads ..... you will still be able to choose the type of boat that suits you.
It's just that the boat toll/tax could be tweeked to factor in number /size of engines in addition to the existing criteria.
If well thought out and implemented it could result in a reduction in toll for smaller, less powerful craft.
It would be foolish to raise the toll for the larger twin engined boat excessively thus resulting in the loss of revenue when they chuff off elsewhere.