Metric-cone conjecture for asymptotic cones of gravitational instantons

Let $(M,g)$ be a gravitational instanton, and let an asymptotic cone mean a pointed-Gromov–Hausdorff limit obtained by rescaling $(M,g)$ along a sequence tending to infinity. Metric-cone conjecture. Every asymptotic cone of $(M,g)$ is a metric cone. The claim is known for faster-than-quadratic curvature decay, but the source presents it as open for general gravitational instantons.