OP makes a good point that areas where new content has been added in the past haven't had to be taken offline/permitted in order for that to happen. Why is the "future content" of the permit-locked sectors different? Even if it's just FDev keeping an option on certain areas, what could they possibly have in mind that requires such an option to be held? It suggests at least one of two things, possibly both:
1) The permit zones have, or will have, a "storytelling" or gameplay purpose. Somehow we can, or will, be able to unlock them, and we just haven't, or haven't been allowed to, yet. The unlock itself will be a big event.
and/or
2) What they are planning to add to these regions is so large and obvious that the idea players could have freely explored these regions previously and missed it wouldn't make any sense. Think systems full of huge guardian cities or planets riddled with Thargoid Surface Sites, things visible from orbit without going looking, and simply impossible to miss.
There is another possibility of course - in the case of the area targeted by gnosis we could be talking a Thargoid bubble. That could mean lots of Thargoid populated planets, stations, and free-roaming ships.