Plastic welding of thin sheet vinyl flooring (hospital grade stuff that I am also familiar with) is one thing, but structural plastic welding of a jet ski hull would be vastly different. Getting plastic to stick to plastic is not always and easy task...and under the jetski operating conditions.....I'm hard pressed to see how it could be done, much less guaranteed not to leak or crack again in the patched area or nearby.
Unfortunately or fortunately....it looks like that's the future of PWC watercraft design.....you know eventually Yamaha and others will find a way to copy Seadoo.
I kinda wish now that I kept my old hull to play around with...but who has the time and the space...not me!