It's a really interesting question.
Imagine if a completely new camera was designed, using modern technology, what a radically different camera it would be possible to make.
Imagine that the ground glass of the optical viewfinder was replaced with a CMOS sensor.
One would not only get a much better viewfinder and assist system, but it would be possible to actually use the videotap for focus and exposure.
And by having predefined profiles on the CMOS sensor, it would be possible to exactly imitate the sensitivity, colour balance and grain structure of the selected film stock. One could also select simulation of different development and processing methods on the assist system, making it truly a "what you see is what you get" system.
Imagine how much less mechanically complicated a film camera would be, if mirror, movement and magazine drive was made with highly precise digitally controlled, direct drive, stepper motors, all being kept in perfect sync electronically.
Imagine using a stepper motor for the movement and a gate that was electronically adjustable. One would be able to select 2, 3 or 4 perf by the push of a button.
Imagine how much lighter it would be, if structural components and magazines was made of carbon fiber instead of metal.
I would love seeing someone having a go at designing a modern film camera from the ground up.