So here is what I came up with. First this is not meant as a 100% failsafe, if your bearing fails bad enough for this (or your axle) to save you, you're Fu$ked anyway. The purpose of this is merely something that in the event of a complete failure may give you a little more time to pull off the road and maybe keep the wheel on long enough to get repaired, nothing more. First an upclose of why I know Im in no worse prone for failure then anyone else.
I took an upclose of the bearing assembly. I've marked the sections with Xs and Os. The lowest O is the spindle/knuckle, where the bearing slides into. The next one is the bearing outer race, which locates inside the spindle. The Os do not move, they are stationary. Now the Xs spin, the first looks to be an inner race and the splined hub. Notice the top X is raised or higher then the surrounding area. That is what the inner axle clamps to. The axle goes through the splined section and clamps to the outer flange where the wheel mounts, which is all one piece of solid metal. What locates the bearing is the outer bearing race bolted to the spindle, and however the internal bearing is made, it is not the axle.
If the bearing went through a complete failure, all the spinning pieces (Xs) would fall off and be still bolted to the back of your wheel. The stationary O pieces would still be on the truck. The axle catches that tiny O lip of the outer bearing race to retain the bearing assembly and keep you wheel on the truck in the event of a failure (though it wouldn't be driveable at that point.) My solution was a simple bracket that functions like the axle in that it prevents the X section from falling out the outside by catching on the outer bearing race.
Here it is installed, again its nothing fancy, its a simple device to add a little bit of safety. Yes it will spin inside the spindle bore at the speed of the wheel.