[bluetidepro]

I don't know too much about how push notifications work, but don't they have some kind of tracking on them? If not, why not? That would seem like a perfect (obvious) solution for what the article describes. If you could somehow track when people take actions on your push notifications, or discard them. Or heck, even if someone decided to receive them, that should indicate that they are looking at them. Mainly because if someone isn't looking at them, they would probably get very annoyed by push notifications from apps they do not care about and thus, turn those notifications off.

Again, maybe I'm just naive about how it all works, but it seems like it could be a pretty measurable metric already?

[dilap]

On iOS, it's pretty much just fire-and-forget. You do get notified when a device isn't reachable anymore, which usually means the app has been uninstalled (so that's sort of feedback). (I think this also might trigger if the phone is offline for a long time, but I'm not sure.)