The semistable slope bound for families of $d$-gonal curves

Let $X$ be a family of $d$-gonal curves of genus $g$, with base $B$ not contained in a certain codimension-one closed subset of $\overline{\mathcal D}_d$. Semistable slope-bound conjecture. The slope satisfies

$$\frac{\delta|_B}{\lambda|_B}\leq \left(6+\frac{2}{d-1}\right)+\frac{2d}{g}.$$

This generalizes the maximal hyperelliptic bound and the semistable trigonal bound obtained from families on ruled surfaces. The codimension-one subset is not identified in the supplied statement, and the claim is presented as a conjecture without a resolution indication.