You've missed the part where they have no intention of replacing it. It's bloat. And I agree with them.
Where relevant they've added stuff as a core part of the panel, like recently an indicator for VPN connections. If you want to use an application you can alt-tab to it, like we've done for decades. Everything else is relegated to media controls and notifications. Appindicators are legacy at this point, and they systematically get cut from modern designs like mobiles.
Notifications, you can have the app fire a notification when it's synced or disconnects for example. Gnome is working on better notifications right now. Tablets, chromebooks, cell phones... have been doing fine without appindicators; people just have a hard time changing their habits.