I have very little use for a camera in my mobile phone; yet I have one, why?
It's because it is so cheap to make a low-end digital camera that it makes no sense to make a phone without a camera.
Even though I'm probably never going to bother using it, I might one day see something sufficiently amusing or important that I would regret not having access to even the poor little camera in my mobile phone; if the difference in price is equivalent to something like a bar of chocolate, of course I'm going to get the phone with the camera.
From the manufacturers point of view; a phone without a camera needs its own variant of the OS which makes no mention of the camera, it needs its own variant of the chassis that doesn't incorporate an opening for the camera, it needs its own printed manuals that make no mention of the camera and so on. At some tipping point when enough people want the phone with the camera it's going to be cheaper to just include a camera with every phone.
I believe it will take several decades to realize, but that eventually the same logic will drive phone manufacturers to include all sorts of things with even the most basic mobile phone.
GPS and navigation software.
Real-time translation from any language to any language; a real universal translator(minus the alien languages).
The Ability to quickly digitize text from an arbitrary surface at an arbitrary angle and read it back in an arbitrary language.
An artificial nose that can detect minute traces of chemicals to help trace a leak, detect minute traces of explosives, record a flavour profile for your favorite wine and tell you what that mysterious spice in your dinner is.
A detector for airborne virii that can correctly place them in a broad category like influenza virus, rhinovirus etc.
A smallish solid-state detector for gamma spectroscopy that is passively operating 24/7 looking for interesting signatures like Co-60(probably a radiotherapy source or food irradiation source that got crushed and blended into a large amount of recycled steel; rare, but it has happened, see the famous case of cobolt-60 in the rebar of Taiwan apartments) or natural uranium(if you happen to find a sizeable chunk of pitchblende or other high grade uranium ore while camping or something, it's not going to be worth much for its uranium content but mineral collectors and other enthusiasts may give you a decent chunk of money for it). It will also satisfy the paranoid itch of people who believe terrorists are likely to try and smuggle nuclear weapons or steal weaponsgrade plutonium.
A 3d digitizer that can create a 3d model of a real world object. It could be used to replicate your face or body shape in a video game; it could be used to scan a broken object or an object that is no longer in production, which can then be printed out on a 3d-printer in the local printing shop in a material hopefully not too dissimilar to the original.
A miniature ultrasound with imaging software and medical diagnostic software that can allow an amateur to monitor atherosclerosis, or explore the bones or other features of your body.
A miniature scanning electron microscope; perfect for amateur entomologists, aspiring sleuths, science hobbyists.
Anything that that is physically possible to make small, cheap and low power enough to include.