This is what happens today. Not in some far off distant distopioan future meant to invoke fear in the ignorant/lazy.

Why not talk with me without the snark? This topic seems like it interests you a lot, so it seems like we have some shared ground.

one can clone the sc[1] and go through the source code for what could possibly define one as a Tails user, replace that with something else, build their own image and voila, you just avoided being in the dragnet.

This won't work because it's extremely difficult to analyze your network card and discover its behavior, and without this knowledge you'd be changing things blindly. There are far too many ways to detect an OS to change them all. Tweak-and-recompile would work if they use a naive and brittle heuristic like "look for the first 64 bytes of whatever is loaded into memory when Tails is booting up," but they wouldn't employ such a brittle heuristic in the first place because every time a new version of Tails is released, they'd need to update their entire infrastructure to look for a new pattern. Something like monitoring the network traffic for a unique "Tails signature" is more likely in this scenario; for example, how many computers start Tor immediately after a network card is connected? Detecting that condition would be a decent starting point for detecting Tails, and they'd want to combine it with some other hard-to-evade condition to cut down on false positives without introducing false negatives.

One interesting way to detect that someone is using Tails would be to notice that their system clock is set to UTC time. Most of the computers connected to the internet aren't using UTC, so UTC time plus Tor usage on startup is pretty commonly associated with anonymity OS's. That said, it seems like it might be difficult for the network card to detect whether the system clock is UTC time, but it's just an example of how difficult it is to fully conceal your usage of an anonymity tool. It's not just a matter of tweaking the source code.

This seems to prove the seriousness of this threat, though. Once you agree that it might be possible for your network card to be your adversary, there are endless ways that it can be used to defeat you. Hardware manufacturers have evidently been thinking along these lines, so why shouldn't we try to think of ways to prevent this from happening? As the BIOS exploits have shown, that dystopianic future may be closer than anyone's comfortable admitting.

EDIT: Someone went through and downvote bombed our whole converastion on both sides... I tried to correct it, but it looks like upvotes from Tor users under a certain karma threshold aren't registering, so I wasn't able to help fix it.