I would like this for the Ancestry.com site. I suggest that each person in the tree have a "quality" scale, perhaps from 1 to 5, where 5 is 100% certainty that the ancestor belongs in the tree(line) and and 1 is low probability but the best shot I have. I would then color each persons "cartouche" based on the rating. A low quality rating would make the cartouche turn red... for instance. This would help me visualize/locate which ancestors I still need to lock down with research.
I usually start with putting someone in my tree based on clues and them do some searches to see if I can either support or refute the individual. Having a color coded quality indicator would keep my tree from getting too messy with unsubstantiated ancestors.