(This seemed like an appropriate place to make a feature request, do tell me if there is a more adequate one)

The need for this feature appeared in this context:
Example: Having a video above a background colour, wanting to blur them together.
Applying blur to them separately wouldn't cut it as that wouldn't blur them together, only individually, and applying the blur to the master tab wouldn't allow me to add anything else on top.
Example's Intended result

Ways to integrate it:
Here are a few ideas on how to fit this into the software

-Option for some tracks to not be affected by the master effects. (wouldn't allow for more than 1 iteration of effects, example: apply an effect to 2 clips and on top of those being 2 more clips with an effect wouldn't be possible)
-Being able to stretch an effect across multiple tracks over there
-Option to apply effects to a group of clips
-Ability to collapse multiple clips into one (possibly allowing to access the clips inside it, much like Blender's Meta strip in its Video Sequence Editor)

I'd be up to the smart guys to decide what'd be the best way to go about it. Thank you all for the amazing work!

The need for this first appeared in this Reddit thread: https://www.reddit.com/r/kdenlive/comments/h89jwg/add_effect_to_multiple_clips_as_if_they_were_just/