Is there a way to use point alpha in the Opacity channels of /mat/diffuse similar to /mat/constant?

To stick with the builder created by the Basic Diffuse gallery preset, dive inside and add a Surface Color node. Uncheck “Use Base Color” and check “Point Alpha” on. Connect the alpha output of the surface color to the opac_int (Opacity Intensity) connector of the Classic Shader Node.

Alternatively, if you switch to the principled shader, you can achieve a basic diffuse material by setting “reflectivity” to 0, point alpha is a simple checkbox on the opacity tab.

Fantastic. Exactly what I was hoping to learn. Thank-you.