Yeah, so select fields (like the workflow) can’t themselves have select fields as properties.
I think if you need more than the ‘basic’ fields that a select database supports, then you would be better served by using a ‘full’ database instead of the workflow/select field.
There are obviously some differences in the behaviour/appearance of a select field and a man-to-one relationship, and there are a handful of discussions about these and related things, e.g.
but if these issues were resolved, I don’t see many drawbacks of using a db.