While the exact amount of detail varies between prints and negatives, any piece of film has a limited amount of detail. However the resolution is limited. So you can get a clearer and smoother image as you go up, even if no new detail is revealed.

And wider color gamut and color depth isn’t the main thing about HDR. Essentially you can go deeper into the blacks before clipping (though your room has to be ludicrously dark to most of the advantages), and more importantly vastly higher into whites before clipping, or I should more accurately just say highlights and shadows. The issue with current display standards is that you lose color vibrancy as you go dark or as you go bright. Max brightness can only be white on traditional displays. The idea is to have such values actually still retain color saturation, allowing for color decisions previously not possible. This could be as simple as being able to have the blue sky of the dat actually look bright, more similar to what you’d see with your eye.

Now the dynamic range of your format does affect the amount of detail you can show off as you can’t recover clipped values in a shot, but the details that do exist can be spread across the whole HDR range. Many modern cinema cameras can now have that level of detail to adapt wonderfully to HDR as recording in flat LOG type formats allow for an incredible amount of light information to be compressed into the footage.

Many top notch 35mm film scans currently in existence, I could imagine have plenty enough detail to support an HDR grade.

A well timed and refined HDR grade of these films from a new 4K+ scan of the negatives has the potential to be quite immersive.

Film scans can often capture the full dynamic range (aprox 13 stops) of the film now, though standard displays lack the ability to display all that range at once with about 5 stops range.