When promoting multiple ideas to a single artifact, aggregate fields that allow for multiple values

Who would benefit?

Everyone using both Ideas and Roadmaps.

What impact would it make?

It would reduce manual updates of possible lost data.

How should it work?

If multiple ideas are promoted to the same artifact (a feature, for instance), fields in the artifact that allow for multiple values should have the new Idea's value added to the current field value, rather than the values being ignored since the field is already occupied.