Finiteness conjecture for optimal subvarieties in mixed Shimura varieties

Let $M$ be a mixed Shimura variety, let $Z\subset M$ be a subvariety, and let $\delta(A)=\dim\langle A\rangle-\dim A$ denote the defect of a subvariety $A$, where $\langle A\rangle$ is the smallest special subvariety containing it. A subvariety $A\subset Z$ is optimal if it is maximal for its defect: whenever $A\subset B\subset Z$ and $\delta(B)\leq\delta(A)$, one has $B=A$. Finiteness conjecture for optimal subvarieties. For every subvariety $Z\subset M$, there are only finitely many optimal subvarieties. This is presented as formally equivalent to the strongest form of the Zilber–Pink conjecture for mixed Shimura varieties, but its status is not specified in the source.