Johnson's bounded-degree Eulerian digraph immersion conjecture

Let an Eulerian digraph be a directed graph in which every vertex has equal in-degree and out-degree, and let the strong immersion relation be the relation described in the paper. For $d\geq 1$, consider the class of Eulerian digraphs of maximum degree $2d$.

Johnson's conjecture. For every $d\geq 1$, the class of Eulerian digraphs of maximum degree $2d$ is well-quasi-ordered by strong immersion.

This conjecture would establish well-quasi-ordering for every bounded-degree class of Eulerian digraphs under strong immersion, complementing the paper's antichain showing that unbounded degree prevents such a result. It was previously conjectured by Johnson; the source gives no resolution.