I'm with Dusta on this and don't see the issue.
If you are that far out and something happens with your lines/harness causing the kite to disconnect - how many people can swim the 400m back to shore?
this new rule isn't going to effect the majority of kiters, with only the racers having to buy a new type of vest (life jacket vest rather than an impact vest).
I do agree though there needs to be some design work on the type of life jackets that can be safely used for kiting.
Any jacket with foam flotation will almost break your neck if you fall into the ocean from height.
there are lots of industries that use inflatable PFD's (personal flotation devices) that would be a better design to use for kiting.
I'm sure someone will cross a PFD and impact vest making a perfect life/impact jacket for kiters (I think I need to get to the patent office to stake my idea).
Steve