I think it's a shame that so many seem so wimpy about koshinage. As a result, few people with less than 10 years experience seem to have their koshinage technique developed to anywhere near the level of most of their other techniques.
In my own experience and working with others - which is by no means vast, but also not insignificant - I have found that almost anyone can take koshinage falls safely, provided they have a good nage. I think distinguishing it from other techniques, making it seem like a big deal, and letting people "just load up" for anything beyond a very minimal time, is a mistake. The fear itself is the problem, and nurturing or enabling it is precisely the wrong thing to do. Anyone with moderate experience and decent fitness can safely O Goshi your grandmother.
It seems to me like the main danger is more in allowing inexperienced nages with insufficient strength and stability in their lower body to participate incautiously. I have seen and experienced a lot of nages collapsing under uke's weight. I say the koshi-aspiring Aikdioka of the world need less exposure to pampering and more exposure to the squat rack.