In the Communist manifesto among other places.

The proletariat will use its political supremacy to wrest, by degree, all capital from the bourgeoisie, to centralise all instruments of production in the hands of the State, i.e., of the proletariat organised as the ruling class; and to increase the total productive forces as rapidly as possible.

Also how would you decide what is “genuinely transitional” and what is it transitioning to?

Organizational structures that undermine the modern logic of private capital accumulation and elevates worker and community ownership of the means of productions either thru local representative bodies or direct control, eventually leading to the abolition of commodity form, that’s what I mean by transitional

China’s regional devolution policies toward local municipal representative party control of state owned enterprises points to an outline of a transitional state in its early stages

Between capitalist and communist society there lies the period of the revolutionary transformation of the one into the other. Corresponding to this is also a political transition period in which the state can be nothing but the revolutionary dictatorship of the proletariat.

Marx, Critique of the Gotha Program (1875)

Not saying this is what China is, but if a vague outline of this transformation does develop because of Chinese regional devolution, well bucko we’re in business