What are the differences between Extending LilyPond and Scheme (in LilyPond)?

AFAICS there is on the one side the work of Urs Liska in this github repository that was forked by Jean Abou Samra (see this fork). On the other side there is a similar work of Jean Abou Samra in this gitlab repository.

And while the repository from Urs Liska accepts issues none of the other repositories is accepting issues or comments.