Oort's amalgamated-sum conjecture for Newton polygons on the Torelli locus

For $i=1,2$, let $g_i\in\mathbb{Z}_{\ge 1}$, and let $\nu_i$ be a symmetric Newton polygon appearing on the open Torelli locus $\mathcal{T}_{g_i}^{\circ}$. Write

$$g=g_1+g_2.$$

Let $\nu$ be the amalgamate sum of $\nu_1$ and $\nu_2$. Oort's conjecture. The Newton polygon $\nu$ appears on the open Torelli locus $\mathcal{T}_g^{\circ}$.

The conjecture predicts that Newton polygons occurring for Jacobians of smooth curves can be combined under addition of the genera. It is attributed to Oort; the source does not state whether it has been resolved.