Allow having several timelines opened in parallel. Requires some work on the current code to make guides and timeline preview attached to one timeline only. First step would be to allow several timelines in the same project (sharing the same project bin).
Brainstorming: one way we could implement this is to add a new clip type in project bin: nested playlist. When double clicking such clip, it would open a new timeline tab where you can add/edit clips.
This 'nested playlist' clip can then be dragged from the bin to the main timeline...
WIKI Project-File-Refactoring: https://invent.kde.org/multimedia/kdenlive/-/wikis/dev/ideas/Project-File-Refactoring/