You would think a good 35mm film would profit from a 4K scan but theatrical prints are at least 3rd generation copies from the original (Original negative, interpositive, internegative) and aren’t as high resolving as the original negative. And the Russian film stocks aren’t terribly high resolving either. The only thing that would likely gain noticably more detail in a 4K scan of a typical print (there are exceptions I’m sure) is the tiny scratches, dust and hair all over it. =)
For example compare some commercial Blu Rays done from the original negative against some done from the interpositive and you might already notice a slight decline in sharpness, and that’s just the first generation master copy basically.