Most common injuries probably include strains, ankles, knees, kiters elbow, etc.. Not sure what single mechanism or small group of aids might effectively avoid or minimize this injuries.
Some of the more serious injuries, such as Traumatic Brain Injury might be mitigated (minimized or perhaps avoided) by a good helmet for kiteboarding. Other injuries such as drowning, rib fracture may be mitigated through the use of impact vests. Is there room for improvement in design of helmets and impact vests/flotation aids for kitesurfing? Tons, innovate away as there is both need and a great deal of room for effective improvements.
Regarding kiteboarding pros, they are generally the last riders you will see wearing this stuff. Because they won't do them any good? Don't think that is the case, must be something else.
You should read through posts at: viewforum.php?f=131
also look at viewtopic.php?f=82&t=12309
you could also search for ricki and helmet or impact for some design considerations and relative attributes to optimize.