I'm currently trying this out, but I run into some error.
When I want to save a content, which contains some image, it raises an error
Field 'blob_id' doesn't have a default value
Without an image, it works fine.
For now, I'm using https://github.com/kylefox/trix/ which works fine and it's simple. But images are saved within the same model.
I suppose I'll wait until rails 6 will be out. (currently using 5.2.2.1)