It would also make sense in developed countries: shitting in water makes it much more complicated to treat afterwards, and greatly increases the ecological foot

It would also make sense in developed countries: shitting in water makes it much more complicated to treat afterwards, and greatly increases the ecological footprint of that processing. Moreover, it makes failures to properly treat much more dangerous (human feces are where you most easily find pathogens specialised in human invasion, besides human cadavers). Feces compost just fine in a dry environment, if you mix it with enough carbon (dried plants or sawdust). No treatment, except letting it decompose over a couple of years, and very little smell if the nitrate/carbon/humidity balance is respected. Of course, water companies wouldn't be thrilled by such a simplification, and people like the illusion that their poo-poo just magically disappears when they press a button.