With the introduction and growth of SUP activities in the waves, it's just a matter of time before things get real messy. With windsurfing and kiting, the presence of wind kind of works naturally to separate the situation at bit from the surfing scene. Surfers normally get the morning and late afternoon glass off to get their fix, so the peace is generally easier to maintain.
But with the SUP thing, they're jumping right into the middle of the surfer's primetime game. The surfer that started this thread is absolutely right about the need for reasonable fairness and balance. From what I've noticed, often the SUP surfers will pick spots that better correspond with their style of wave riding, and that's a good thing overall. This approach to things makes good sense, as it allows things work with much less potential conflict.
However, at the better spots (faster, more critical breaks) where significant crowds of surfers congregate, I think that SUP surfers need to be especially cautious and thoughtful if they want to fit in. It doesn't take too many SUPs to effectively dominate a lineup and sow the seeds of deep discontent. Surfers are quite a steely and determined group that doesn't always hold back their emotions and actions. Believe me, I know the scene quite well having been a dedicated surfer for over 23 years before starting windsurfing in the mid 80s.
There's always a sensitive balance in the lineup that needs to be maintained to preclude trouble. As long as the SUP folks understand that, then a relative peace can be maintained.