D'Annunzio was seen more as a revolutionary than Benny (the king and the rest of the enstablishment thought he can be controlled) and if he try an analogue of the March on Rome, VEIII will give the order to shoot, plus he don't have the attention neither the desire to do the gritty and boring day to day political stuff necessary to create something like the PFI, he will not succeed in bring together the so different group that formed his powerbase and/or play one against the other.
Even if he, for whatever divine intervention, get the PM job...he will soon leave any serious political work to his deputy and occupy his time with booze, drugs, women and/or some spectacular endevour as his attention span was very brief