Ah, you’re right. I tried it on a skeletal mesh and it didn’t look good. I fixed it by duplicating the mesh and assigning it an opaque material. Color doesn’t matter. On the mesh component, turn off cast shadows, turn off Render in Main Pass, turn off Render in Depth Pass and turn on Render CustomDepth Pass.
What this will do is render a proper self occluding version of the mesh in the main pass into the custom depth buffer. This allows us to correctly draw the transparent mesh. Note that this will occlude any transparent objects behind this mesh that also uses the custom depth buffer.
As for the AA dithering version, I think the motion blur can be removed by using the same technique. I think the messy blur is because the motion vectors are only written on every second pixel. So if you add a duplicate like above, it might overwrite the motion vectors. If you don’t want to write to the custom depth, it might be possible to use a translucent material with opacity of 0 and enable writing the motion vectors. Not sure if this would work, but might be worth a try.