While everyone is of course free to start his/hers project there is a whole bunch of projects which basically does the same thing like: deduplication, client can append backups only, server side client backup rotation / pruning, etc.

For example restic ( https://restic.net/ ) does everything the author describes in the ideal feature set ( https://packnback.github.io/blog/work_begins/ ) except for asymmetric encrpytion. Though there is an issue open for that and iirc they are working on it. Contributing to that project would probably be easier?

Another existing very interesting project to contribute to is rdedup ( https://github.com/dpc/rdedup ) which is written in Rust.

There is a whole list over here of existing backup solutions: https://github.com/restic/others

Judging from the comparisons made in the introduction blog post by the author I think he / she missed the existence of a bunch of existing solutions.

EDIT: This was supposed to be a reply to the comment in which marmaduke asked "why start a new project?"

> client can append backups only

You mention Restic but I don't see how it enforces append-only security. According to its S3 documentation[1], Restic requires PutObject, DeleteObject and ListBucket permissions.

[1] https://restic.readthedocs.io/en/stable/080_examples.html#se...