I don't think it's all that 'weird' to list one of your opponents as your intended nomination for a Cabinet position. It's perfectly reasonable to share similar viewpoints with someone in one particular policy area, but different viewpoints in others — or even to share similar political opinions but promise differing leadership styles.
I'm open to the Cabinet nominations announced during the campaigning period not being 'final' — I think there would be a political cost to swapping out what people voted for without a satisfactory explanation, and I'm sure it would come up in confirmation votes.