Are in-camera ND filters provided by physical lens elements or by firmware?
As for camera features nobody would use, I'd rather have built-in ND filters than any of the following common camera features that I never use:
o Video - I use the video function on my DSLR on a regular basis when I'm out with the family, its a great feature.
o High ISO - I use that almost every time I take a camera out and it is one of the major advantages of a digital system over film - I can't conceive of going back on a permanent basis.
o Flash - Extremely useful feature not only for popping a little catchlight in, helping with a quick balance but for triggering external Speedlights when I don't want the hassle of triggers. That and just about every mainstream camera in the last 20 years has had one so its not even a 'thing' to discus.
o Wifi - If I had it I would likely use it but no its not a major selling point for everyone, but it costs essentially nothing to add as even a £20 phone has it.
o GPS - Wish my Pentax had it instead of an addition as I would use the built in star tracking feature more often.
o In-camera editing - Goes together with the Wi-Fi to allow instant sharing, something that is ever more common.
o Sepia, black & white, and other color modes that can be easily achieved in post - Reviewing and even better previewing your shot in mono can help greatly when creating it. If you shoot RAW and like mono images it is a very useful feature.
o Red-eye removal - For people who use a camera for fun it is a great and very simple bit of firmware that you set and ignore, for the extra few lines of code why not have it?
And yes the ND filters are a physical and mechanical addition to the lens.