Currently assets do not have any user-definable metadata like this, I guess because that would make them a lot like packages? Assets also aren't intended to be like a "SharePoint replacement", which is why we don't want to put a lot of extra features like versioning, etc. These are also hard to replicate, etc.
That being said, we are open to changes, so please consider using the Feature Request Process. Note that, we also want to evaluate "why" and "how this would be used", and that's part of the feature/change process.