Unfortunately that feature wasn't carried over from Marvel 1.x to Monitoring 2.0. One of the big reasons why is that indexing every cluster event required a lot of disk usage and there was no built-in way to clean up old data (but it could be done by configuring Curator).
Monitoring 2.0+ started with a much more limited set of features but the tool is now becoming useful for cross-stack monitoring, such as dashboards for Kibana and Logstash. We're also working on other features that will hopefully not let users miss Marvel 1.x too much.
I would love to see something like the shard allocation timeline player come back to Monitoring, and the conversation does come up often, but we have no ETA on when that would be released. Hopefully the work we're doing on built-in data curation adding more decisions into what kind of data gets indexed and how often will take away the problems with indexing too much data, and that would put us in a better place to re-introduce this feature.