Analytics is currently in preview. You can see data on how your app is performing. One indicator that is available is the time it takes to get to the first screen. Below is a screenshot of the time it takes to get to the first screen in seconds. If that information is already readily available and recorded for each user's instance, I would like that information passed to the app.
In my app, I want to tailor the experience to what a user's device is able to handle. My Surface Book can run everything 100% with timer controls running on time, but my users don't all have i5s and i7 chips.
So as of yesterday, I have currently programmed a variable in which I measure the time it takes to cache data from the OnStart operations. I create a Toggle that returns true if the elapsed time it takes to perform the OnStart commands exceeds a benchmark I calculate from the average load time in analytics. I 'throttle' or reduce the content that is returned to the user if the Toggle is true; it's not an ideal solution, but some of my apps are unusable if the user's device can't handle the writes, rewrites, images loading, etc. at a reasonable speed.
But not all my apps have OnStart commands to be a good measurement of performance. The time it takes to load the app is the perfect indicator.