Hello!
Currently, when you try to add a property with 3 dimensions (i.e. the position or orientation of a 3D layer) to the Essential Graphics panel After Effects returns a "Property Type Not Supported" error. This is not a huge limitation, as you can make scalar properties like sliders on the layer and link each slider to a component of the vector property. However, this requires 3 rows in the EG panel rather than the slicker 3-dimensional vector interface we're used to.
Thank you for considering this request!