It really is only significant because of how the players are using the space now. If Niarja had been 0.4 security from the beginning, the use of space by players would be different, but the game would be just fine and largely the same as today.
So yes, it is a significant disruption from the current status quo, but one that was completely intended. CCP wants to shake things up and force people to adjust to a new, changing environment. No one, including them knows exactly how players will adjust to this particular change, but let’s not act like this is a major change to the core rules of highsec, or the core game itself, like our friend there in the OP.
Once things settle, highsec itself is almost exactly the same - just reshuffled a bit and a fraction smaller. The most significant thing about this is that it sets the precedent that things can actually change now, and while I get why some people find that thought scary, I agree with CCP that static inputs produce static outputs. So while there is such a thing as too much chaos, we have been suffering a little too much order for the last decade and it is time for a long overdue shake up.