You can, but every hardware feature you add takes physical space in the phone. Making a phone waterproof requires adding stuff to the phone, which takes away space for other things. Usually battery size ends up being one of the things that takes a hit. You want a phone that’s waterproof and has a removable battery? Then the battery size gets reduced by X%, or some other features people care about get dropped.
I doubt that. There’s already a lot of other features out there that have to be region locked because of local laws. Could be medical related, car crash detection, etc. The cost of an engineer just reusing that same logic would be fairly minimal.