Currently, PBR reflection probes are transparent only. My suggestion is to allow the faces on Reflection Probes to be texture-able. Reason: Often when decorating or creating a new build, users will utilize a prim to create the floor or wall (and especially in the case of a Linden home to re-texture the floor/wall with carpet or wallpaper). Allowing a Reflection Probe to accept a texture on any given face will allow users to utilize a floor, wall, or ceiling of a room that has been properly "Sliced" or "Hollowed" in the object edit menu as a Reflection Probe without the need to rez a whole new prim for the probe alone.