Boundedness of analytic slopes of holonomic D-modules

Let $X$ be a complex manifold and let $f$ be a holonomic $f$-module on $X$. For each hypersurface $Z$ of $X$, consider the analytic slopes of $f$ along $Z$, namely the real numbers $r>1$ for which the supports of the graded pieces of the irregularity filtration along $Z$ are nonempty. Boundedness conjecture. Locally on $X$, the set of analytic slopes of a holonomic $f$-module is bounded. This would provide a characteristic-zero analogue of bounded ramification with better functoriality properties; the source presents the uniform local bound as not clear a priori.