@gryff, thanks. This ties into an earlier question when I was trying to even get export working at all without clipping for textures with alpha.
PBRMATERIAL_ALPHATEST got me the same as STD materials. I now want better. Think I am going to have to go through a 4 modes. I seem to remember PBRMATERIAL_ALPHABLEND did not work right. Think because the exporter is setting everything the same.
May need to add a custom property to the materials section of the exporter to allow setting the transparency mode, or set the material._alphaCutOff, in which case you are screwed in the .babylon exporter cause it is not serialized.
@sebavan, is there a reason alphaCutOff is protected & not serializable?