I also want headphone jacks back - which I'm sure will be less popular here than batteries. We used to have waterproof phones with both.

I'm not sure about the rules around required ability but I'd like that too

I've come to realize (I think) that this actually does have a lot to do with waterproofness ratings -- a legibility trap.

I notice that Fairphone excludes headphones from their latest devices, and attributes it to the necessary of doing so in order to get an "IP55" rating.

I'm not sure if that ultimately makes sense (and suspect that it... doesn't), but the legibility trap of that ratings system might actually be part of the cause of the current market absence of a feature so many people still talk about after years of its unavailability.

Phones back then were definitely not as durable as modern ones. Whether you like it or not, it's easier to waterproof a completely insulated system.

Every phone should have a SCSI port with an included terminator in the box.