i am not much interested in the sleep features, BUT i would absolutely love to have an upper arm HRM from Garmin. There are only a couple devices on the market and nothing was released recently. I bet an Elevate v5 would work with great accuracy..
My naive guess is this can’t be too complex: Garmin needs to increase the battery capacity a bit (should match Fenix battery runtimes, so 30+ hours) and develop a new band.