Would everyone on the network be able to predict which user will create the next block? If individuals can predict when they will create a block then they can cause a bit of trouble. Users can't single handedly create an alternate chain, but if they had a small group of individuals buy almost the same amount of coins at the same time (to start timer), they would potentially create blocks in order. This could allow a small group of individuals to create their own malicious chain to take advantage of the system.

There is a very high chance I don't understand your paper well enough to comment, but the above is something I was thinking about and wanted to share.