This is true, I use Contabo as my host actually didn’t know they had OBstorage too 
But when it comes to write a plugin, they are saying S3-Compatible API so I presume URLs etc are the only thing that changes.
Might be worth check that it has an API you can use if so what are the docs, and could write a plugin for it.
I wrote a plugin for S3 myself so as @DavidWitten said it should not be to hard to modify it.