1) I see Kamal was an inspiration; care to explain what differs from it? I'm still rocking custom Ansible playbooks, but I was planning on checking out Kamal after version 2 is released soon (I think alongside Rails 8).
2) I see databases are in your roadmap, and that's great.
One feature that IMHO would be game changer for tools like this (and are lacking even in paid services like Hatchbox.io, which is overall great) is streaming replication of databases.
Even for side projects, a periodic SQL dump stored in S3 is generally not enough nowadays, and any project that gains traction will need to implement some sort of streaming backup, like Litestream (for SQLite) or Barman with streaming backup (for Postgres).
If I may suggest this feature, having this tool to provision a Barman server in a different VPS, and automate the process of having Postgres stream to it would be game changer.
One barman server can actually accommodate multiple database backups, so N projects could do streaming backup to one single barman server.
Of course, there would need to be a way to monitor if the streaming is working correctly, and maybe even help the user with the restoration process. But that effectively brings RTO down to near 0 (so no data loss) and can even allow point in time restoration.