Kdenlive is refactoring its timeline to be based on Qt's data models and a QML view. This work is not yet finalized so any help there is appreciated by the developers.
There is a board tracking the current blockers for a first release with this new timeline: https://phabricator.kde.org/T7128
The work is not limited to the items on this board though: there is space for working on optimizations of both the model and the timeline itself as well as finishing the implementation of things like effects, transitions, etc.
This project is one of its kind!