> It is a binary file optimized for both space efficiency and quick access. Since then, it has been possible to create a repository that uses a reftable rather than the old file-based mechanism,
Good, are there (m)any other plans to ditch the slow files and use proper database? Or is it only reserved for various post-git competitors?
> Good, are there (m)any other plans to ditch the slow files and use proper database?
The filesystem is a proper database, just not a relational one.
Linus focused heavily on performance when he wrote git; he used the filesystem because, as the main Linux kernel maintainer, he knew that the Linux VFS and filesystems were fast enough for these use cases.
(It's the use cases that have changed; it was not expected back then to have more than a few hundred refs in a single repository.)
It's not just slowness, but what about case insensitive filesystems?
By "proper" I assume you mean relational? Or ACID? Or you mean using existing database software? What is so improper about the way git stores data?
Yes, Patrick Steinhart (GitLab) has been working not only on reftables and pluggable backends for the references data, but also pluggable backends for object storage, so that you can use any database backend format (sqlite, s3, special large file storage options, etc) to store objects if you want (in addition to loose objects and packfiles).
This is work that Patrick and GitLab have been doing for years now and it's very impressive and nearly complete.