People want IP ratings. What same people don't understand is that most phone makers tell you it is not permanent. And same people also don't understand that IP ratings are not ratings of waterproof-ness (which, by definition, would not need a rating).
They aren't mutually exclusive at all. You can even have a real headphone jack and maintain a high degree of waterproofing.
I think eliminating the ability for people to replace batteries and use SD cards has more to do with saving manufacturing costs and encouraging people to replace their phones more frequently.
I'm not sure that it needs to fully turn off, many of our electronics don't have that ability. As long as it has power it could run in a super-low-energy mode that just keeps a capacitive sensor going.
On a related note... come on, phone manufacturers! That's enough with sealed phones and a lack of microSD card slots for added storage.
Also, come on, app programmers! Let users store data in a microSD card, instead of in limited, expensive built-in storage! If you can't find the data when the card is removed, just deal with it! (I'm looking at you WhatsApp, given your insistence on storing photos and videos on internal memory.)