Love Card View! I can definitely see using it. My issue is that I do almost all of my viewing in Reports as opposed to Sheets because I work across many sheets for my work, consildated into Report views. I know there might be complications to implementing this, for example when a sheet included in report does not have a given column, but it seems there could be a way to deal with that. For example, putting rows/cards into the Uncategorized column, and not allowing drag & drop from the column. I can understand why you did include Reports in the initial release. Please put my vote in for this enhancement.
P.S. You might want to add "Card View" to the Functionality checkbox list when starting a new discussion, as there are checkbox for some of the other types of views: Calendar, Gantt Charts, Sights (but not Grid View).