I guess most linux users interested in video NLE know some basics about cinelerra.
In cinelerra there's a distiction between realtime and rendered effects.
There's no doubt I can get similar stuff out of kdenlive with additional effort.
But it tedious housekeeping and distracts from the main editing workflow.

IMHO, having an integrated option for pre-rendering effects into some sort of cache
exhibts two main benefits.
- Editing Speed-up in case of resource intensive effects, which won't run in real-time
- Ability to use video effects with inter-frame dependencies like some sort of integration (over time). Worst case (in case of dependencies ranging back to frame 0, e.g. integration) playback cannot be started at arbitrary frames. Pre-rendering is a must. Furthermore, frame-dropping in favour correct playback speed is impossible for
video effects with inter-frame dependecies.

Dynamically pre-rendered cache files could also be utilized as some sort of resource preserving low-res previews of HD clips. Storage might be either full resolution, uncompressed, lossless (huffman,ffv1,mp4 lossless) or low-res lossy (just for basic display during editing). Full reolution lossless would be slower requiing way more disk space at the advantage of possible re-use of cache files in final rendering.

I'd prefer to rerun effect rendering at full resolution during final rendering and just store low-res previews based on lossy, relatively fast compression. Ideally, this descision might be exposed to the user. Let him choose codec and sub-sampling ratio of cache files.

From a GUI and handling perspective a simple check-button at clip or effect properties could selectively enable the dynamic creatation (autoupdate yes/no) of cache files.
Effects with known inter-frame dependencies should have an option to enforce pre-rendering.

Now, that was my cent on chache files and I'd probably put it on my wishlist for christmas. What do other users think about cache files ?
May some of the developers comment on expected implementation complexity.

GUI work could be low and depends on the configuration complexity kdenlive offers to the user (-> config dialog). Components required for file generation should be existing. But handling the cache files may require to establish some sort of database. Here I've got no clue about the minimum work required to get things working smoothly.

Just "brainstorming" ...

Toby