We show that the CM line bundle on a proper family parametrizing specially K-stable varieties with maximal variation is big and nef. As an application, we show projectivity of any proper subspace of the coarse moduli space of uniformly adiabatically K-stable klt-trivial fibrations over curves constructed in Hashizume and Hattori (Geom. Topol. 29 (2025), 1619–1691).
Masafumi Hattori (Fri,) studied this question.