When I am working with clients on projects, we communicate through the 'Note' function on the platform. This is how they tell me when candidates have progressed to a new stage in the interview process, who that interview is with and what date it will happen on.
I think it would he handy to have an integrated inteview calendar for each position. It should be toggled on/off so client's dont have to use it as can see it being annoying for them. But would be an easy way to visualise the process.
I think there should also be a master calendar for across all projects.