The issue with deionized water isn't what your GI system will or will not absorb. The issue is that the water may absorb minerals and nutrients from you.
I have to imagine that this is easily combated if it proves to be a significant factor. Worse case scenario, now that you have water that doesn't make you violently ill, you have more energy to farm/eat nutrient rich foods?
We are talking about trace quantities of salts though. You could get around any measurable problem by passing the water through a large box full of pebbles. Also, water is for agriculture as well as drinking, so this should increase the stability of food supply anyway.
I have to imagine that this is easily combated if it proves to be a significant factor. Worse case scenario, now that you have water that doesn't make you violently ill, you have more energy to farm/eat nutrient rich foods?