Long time Pebble fan, and currently have a Pebble Time Steel, a Core Time Duo, and a Pebble Time 2 all connected to the new mobile app.
One thing that’s happened multiple times to me is realizing mid-afternoon that I didn’t get any notifications all day because I’d forgotten to change the watch that’s active in the Pebble app. I’d love to see a “auto-connect” mode where if the app isn’t able to connect with its currently selected device, it would then try connecting to the next-most-recently used one.