People have been complaining about NAT for decades. It's time to STFU. It's a well-known problem with a bunch of well-known solutions.

If you don't like NAT you could go IPv6.

But really, why do you need to talk to your device? If it's just reporting in NAT is irrelevant. If you want to do device management just write something into your protocol to check for updates/commands and deal with it on a periodic basis. You can even do that on startup, so you can tell the customer to power cycle the device. It's unlikely that any IoT device needs instant updates, so long periodic updates are probably fine.