I think this was inevitable, the original route past Buckingham Palace and though the royal park was always going to cause many problems, given the tourist burden, many ceremonies and frequency of special works for functions. Blocking it on the grounds of the needs of both locations makes the whole expensive scheme questionable.
It's a typical conception of the sort of advisors that Boris Johnson has appointed, impractical and amounting to little worthwhile. As a result we will have two hopefully safe but short mini-superhighways covering parts of the route, with high danger level conditions at the start, through the middle and during completion of journeys.
.