I searched for this option and didn't find it, so I hope this feature request really refers to feature that's not available in vMix now.

When I have a video file input I'd like to be able to set starting and finishing point of the video. The video would play from and to that points and not from the start and finish of the file.

This function would be the most needed when recording delay files. The (for example) 20 second clip never contains the exact portion of video that I'm willing to show, so I need to set the slider every time I want to play the clip and switch to next clip in the right moment.

And how comfortable would it be to set create a highlight playlist (with playlist option), after setting those starting and finishing points.

+1
Shortcuts can be used to mark these points
Start point = crtl + i
End point = crtl + o
and a list of video would be automatically recorded.

Mauro