Awesome post! as for soy milk instead of milk, i really haven't thought of that! but sounds interesting and worth a try!
I personally think any medium can be used to make kefir from kefir grains as long as you feed the kefir grains what they eat. Milk kefir grains eat lactose while water kefir grains eat fructose and glucose if i'm not mistaken.
As long as they have their food, and the environment is suitable, albeit not acidic enough to kill them, they should be fine. Healthy kefir grains are hardy little critters.