Dave I have noticed last week Royal has no listings for San Juan. I was looking last week to see if they still had the zipline listed and saw that they have nothing at all listed. All the excursions are listed for all ports except San Juan.
If you do end up doing that zip you will have to let me know how it was.
Segway and Horseback riding are on my "to do" list.
Also I would not book any excursions from an outside company for San Juan since the Explorer is only in port from 8 to 2.