Notification in the Model Navigator showing which devices are online

I have a few projects where I have deployed multiple devices at once, and it seems like there no easy way to see, at a glance, which are online.
I think some kind of notification in the Model Navigator, possibly by the settings button of each model / device that shows those that are on and offline would be really useful.

Is there a way to do this already, without opening up each device individually?

The Build API is your friend. You can grab a list of your devices and check which ones have a powerstate key set to “online”.

You don’t have to build an app to do it: how about an imp connected to a bank of NeoPixels, one for each of the your other devices? The monitor imp’s agent makes periodic HTTP requests to Build to collect each device’s status.