We currently iterate over the bitbar projects checking for pending tasks on taskcluster and starting tests on an as-needed basis. I've recently deployed a hot-patch that queues up tests equal to twice the number of devices in a device group to help with the issue with short lived superseded jobs. See bug 1563307.
Each bitbar test takes 10-13 seconds to start not counting the other auxiliary tasks involved. As the number of devices in groups grows, the time to completely start tests for each device grows as well and is now over 15 minutes for perf p2 and g5 projects with the pre-population of tests.
We should convert the test run manager into a multi-threaded script which runs each project on its own thread so that they do not have to wait for other projects to be processed.
Side Note: Using autophone's old component for android-hw @ bitbar since it is already available and why not let autophone live on even if in name only. ;-)