As written in https://horizon-eda.readthedocs.io/en/latest/why-another-eda... changing the way how a PCB design tool handles libraries would certainly require a complete rewrite as the library structure permeates the entire codebase.

Starting from scratch also allowed me to trivially implement features that KiCad is missing, such as proper panelisation: https://blog.horizon-eda.org/progress/2020/04/05/progress-20...