I very well could be missing something that already exists, but when I'm running the spatial join, I'm using the field map merge rule "join" to string or list together text attributes into one field. I can successfully do this, but my text is a running mess of letters without separation by commas or spaces, like so: RESIDENTIALMIXEDUSEINDUSTRIAL. Would be nice when running spatial join to be able to tell the output to separate unique values with a comma and a space, like this: RESIDENTIAL, MIXED USE, INDUSTRIAL. If this is already possible and I'm missing it, please do tell. Otherwise, I strongly suggest this be an added feature. The ESRI support rep I spoke with on the phone did not know of a way to do this, but we both may be missing something.