RE: SUP on an old longboard, my experience..
The idea of poling for propulsion is quite interesting. If the wind was to back off in a location with relatively shallow depths, the opportunities could be great. If one was to think about fishing strategies, I'm sure that one could experience options that many couldn't easily replicate. Without an engine, your stealth and cunning would possibly yield some really impressive results.
The SUP thing is quite a multi-faceted format. One can easily customize proplusion to suit different interests. While my focus is a bit different in nature, I can appreciate other creative options. It does open an unexpected door in so many directions.