That was a lot of ignorant crap spouted out there. Let's sort the shit into different piles and identify it:
1) Virtually all "smart home" devices are not "dependent" on the internet, this one included which will continue to function as a thermostat going forward.
Err... except that it IS dependent on both the Internet and the vendor to be anything more than a dumb thermostat, and those extra features are why it was purchased in the first place.
2) Without an external server manage a session for you your device instantly is not suitable for 99.9% of the population who don't have external routable IPs,
If you don't have a routable IP, you don't have an Internet connection.
3) or any idea how to configure port forwarding on a router,
There are services available to broker the connection between your home server and your mobile device through a secure tunnel. And they're pretty much 'click here' to get up and running. And yes, you pay for that, monthly. And if they shut down, because they're an add-on and not part of either server or client... you can find a replacement service to handle it.
It's really dumb to just make dumb posts on subjects where you clearly don't have a deep enough understanding to discuss them intelligently.