I have watched dots on TABR. I think PBP will be difficult to dot watch unless the dots are very small. There are some visualizations online of the sheer mass of people on PBP and the distance they are along the course. It's a moving Gaussian distribution.
http://www.gicentre.org/pbp2015/
select "progress chart (animation) and hit update chart. It's a lot more fun if you know someone riding and their number