Normal-subgroup automorphism dichotomy conjecture

Let $S_g$ be a closed orientable surface and let $N$ be a normal subgroup of $\operatorname{Mod}(S_g)$. Normal-subgroup automorphism dichotomy conjecture. Either

$$\operatorname{Aut}(N)\cong \operatorname{Mod}^{\pm}(S_g),$$

or $N$ is isomorphic to a right-angled Artin group. The source gives examples motivating this dichotomy but no proof of the general assertion.