trying to to tie a follow focus motor to a ultrasonic rangefinder has been done with varying degress of sucess. maybe good enough for T2.8 ot 4.0 with S35mm film, but not good enough for 4K+ and wide open. There is zero reason we can't have focus motors in cine lenses. Sure they would have to be a lot bigger to move the mass, take some power, but so what. those are pretty simple engineering problems to solve.
the real problem, which even a millenial at a show a few weeks ago gave me gave me was " we use manual focus in film" coppng a serious attitude I must be some rube after I said when are you going to put AF focus motors inside this well know cinelens brand. She didn't even stop to realize i've been literally shooting longer than she's been alive. when a I'm not even that old DP could see value in AF this harkens to perception and attitude rather than practical application. Remember film vs digital arguements ? especially the ones about how digital could never replace film ? um, ya right, we know how that turned out and AF in cine lenses is exactly the same arguement and mentality all over again. can we skip the middle part and just get AF motors in cine lenses and be done with it ? or at least external FF motors designed to do that job and talk with the camera bodies via generic standard protocol so everybody's gear plays together like MIDI ? sigh !