Translucent particles for billboards and ribbons are sorted on CPU, of course overlapping quads might flicker but sorting should be correct. For meshes though it is not implemented as the only materials exposed in Pk-Editor are additive (no need for sorting), solid and distortion.
No real reason except that we never really tried to render meshes with a translucent material in UE4.
Is there a reason why a Masked material wouldn't work instead of translucency for this effect ?
If really that would be a need on your side, we can discuss implementing that in the plugin.