I would like to have a shared state (list of clients fetched remotely) between 2 sibling Routes : Timesheets and Clients. I want to try how far
Timesheets
Clients
You can take a look at reacts Context. Redux also makes use of Context. It allows you to pass some data down to all children. But you should write code to use this data, for instance you have determine contextTypes etc.
You can see details on docs about how to use it.