The demand for such an aircraft would be extremely limited, and confined to areas with a large volumes of smooth water, mostly inland lakes. Australia is one of the driest continents on Earth and as such, contains very little by way of large areas of smooth water suitable for such an aircraft, so virtually no demand here. North America and Canada would be the areas with a small potential for such an aircraft.
Amphibians are quite restricted as regards rough water and wave heights (and winds, which are normally higher across expanses of water), so they start off with serious use restrictions before you can even start to define their area of operations.
I fail to see where an aircraft of this design would promise great usefulness.
Are you proposing a rescue unit that is capable of major water rescues? In that case, if the jet ski operator finds survivors from a marine disaster, what is the jet ski operator going to do with the survivors?
Multiple survivors need to be taken from the water to a life-sustaining situation, so that means a liferaft at least - but it's better that they're taken to land, or another large watercraft that is close.
I cannot see a situation where this design would provide a high and effective level of rescue ability, as compared to fast rescue boats, that would be much more capable of rough water operation. Remember that poor weather is responsible for many disasters, and aircraft operation is limited by poor weather. Add in rough water precluding the use of a small amphibian, and the field of operations is very small.
The flying boats of WW2 were very capable of water rescues, even in open sea conditions - but these were extremely large amphibians, and shared more on-water abilities with boats, than a small amphibian would.