It's more of a "accessibility layer" on top of S3 or any other s3-compatible backend (which means that it also works with MinIO out-of-the-box [0])
I don't think we'll ever build the underlying storage layer. I'm a big fan of what the Tigris[1] team have built if you're looking for other good s3 alternatives
1. You buy the storage from Amazon so I pay you and don't interact with Amazon at all or
2. I buy storage from Amazon and you provide managed access to it?