Grabbing and disabling a fast runaway kite , in theory anyway, is very dicey, perhaps even infeasible in many cases. Of course if the leading edge slams into you there is something relatively soft to grab. Then again if you are in the path of a fast moving runaway kite you are putting yourself at risk of some serious line cuts. In the case of the lines,or the bar, I don't think anything of this type is well advised. The line(s) of a FAST moving kite could slice into and perhaps through fingers from friction alone, perhaps even through gloves. In grabing the line you will initially power the kite back up as well. If the line wrap a finger or wrist, it would seem a severe cut would be hard to avoid. If you grab the bar it will likely power the kite up assuming the bar doesn't rip your hand off. Slow moving kites may present other options but it is a case to case thing.
The best solution as in the case of what to do once your car piles through a guard rail and is flying off an alpine cliff, IS TO NEVER BE THERE IN THE FIRST PLACE. Once something like this is in motion there may be few ways of safely dealing with it until the kite has flown its course, done its damage and has become shredded or disabled on its own. So what is the solution? Riders need to use and properly maintain, test kite leashes. Otherwise get ready for possible cliff sailing in your favorite ride as you will be setting the table for that possibility.
Some ideas on dealing with runaway kites appear at:
Vesku your point about hypothermia in the coming cold months is a good one. I recently read an account of a windsurfing that went out in marginal exposure clothing, a shorty wetsuit, in colder conditions, things went wrong and he was disable in the water for an extended period. Unfortunately, exposure claimed this windsufer. Exposure is a potential issue in most waters, at least above the tropics. You have to generally work harder to have exposure problems in South Florida but it is possible. In more temperate and higher latitudes, I imagine it can be a real reality. So not only do you need to know your stuff about kites, wind, weather, waves, currents, etc. etc. you also need to anticipate things and come prepared with proper exposure clothing for your local conditions.
Shred hard and stay warm!