Additional render options for "sparse" animation renders

Random idea, curious to see if anyone else likes this. Currently you can set a "step" in the frame range in order to render frame 0 , 10 , 20 , 30 , 40 etc. This "sparse render" is really useful for previewing what your full render will look like at various points in your animation, without having to render the whole thing in full granularity.

I've been thinking about some additional "sparse render" options that would be useful:

• "fill" sparse renders - in the example above, after rendering frame 0 it would copy that frame to 1 - 9 ; then render frame 19 and copy it to 11 - 19 , etc. That way you'd have a full render (deliberately choppy, rendered "on the tens" that you could play in your favorite NLE editor against audio and comp against live footage etc.
• "render only keyframed frames" where it would only render the frames where some object or rig had been explicitly keyframed (skipping "generated" keyframes). This would let you see renders of your key poses
  • and a "fill" mode for this
• "progressive render" where in a 1025-frame animation it would render in the following sequence:
  • frame 0 , 512 , 1024 (first, middle, last)
  • frame 256 , 768 (the halfway point between each of the rendered frames)
  • frames 128 , 384 , 640 , 896 (the halfway point between each of the rendered frames)
  • etc
  • and a "fill" mode for this
  • this would progressively fill in a sparse render so that impatient people can view their ongoing render in increasingly smooth animation as the render progress

This is all probably a silly idea. But sometimes errors are apparent in the final render that don't show up in viewport animation or viewport renders. The good news is, it can be implemented in a python add-on without having to modify core Blender. I might do precisely that on a rainy day. Let me know if you think this would be useful or have other ideas along these lines.