I have seen similar requests among the ideas, but not quite this "ask." We need a single custom field to be shared among several product lines so that we can use it in reporting. Right now, we have the same custom field in each product line (created separately, but the same field recreated). When you go to report on custom fields among various product lines, they are treated as separate, so you have to pull in the same custom field various times to see all of the content. We need them to be the same.
This can be achieved today by creating a custom field at your highest product line level.
By doing this, you can have a single custom field which applies to all products, and be able to report on this single object across all products and product lines.
What about outside of a product line? Can we have a custom field shared outside of the product lines?