when I will be able to use my OneDrive as a drive to store my Win10 backup ?

Ah, you mean File History...

Well, I don't know if it will ever be possible to store File History data in OneDrive.

But, on the other hand, for the files stored in OneDrive you already have Version History, hence you could perhaps move your default data folders (Documents, Pictures etc) to OneDrive, obtaining, therefore, a similar result.

See https://support.office.com/en-us/article/sync-your-documents-folder-with-onedrive-0f4ddfd3-4a72-4013-9d94-181dab6be19a