It would make my wedding workflow so much easier that I can keyword like this: 1-prep, 2-ceremony, 3-portraits, 4-details, etc. That way I can put them in the order I want, rearrange if need be, renumber and then remove those keywords.
You can already do this with a work around. Color labels are stored as text in a special metadata field. You can enter another text (not associated with a color label) in that field as well. Lightroom will simply not show a color label in that case. Then in Grid view you can sort on 'Label Text'.