Right now we have regular and linked frames.
I would like to propose third options for the frame handling which would work similarly to the linked frames but instead of linking to a user defined keyframe, it would link to one frame before the next keyframe.
If you have timeline with 8 frames total, and with keyframes on frames 1 and 5.
then the image from keyframe 1 would be linked onto all empty frames coming after it until frame 4. Then again from keyframe 5, the image would be linked all the way to the frame 8 which is last one in the whole animation.
To try the behaviour for yourself, try blender grease pencil or the timeline in krita, both are free and open source programs.
why: It saves metric ton of time when animating straight ahead or doing the inbetweening and it’s very intuitive to use.