is it possible for ESO to evolve into an open-world pvp by this I mean for example being a nord and going into aldmeri territory or vise-versa

That as said many many times over is against the design goals of the game. There are many threads on this subject.

Cyrodiil is a massive zone in the center of the map. This is where all 3 sides can see each other and fight over territory. Each side has there own home territory within Cyrodiil so you can go to the enemy's side and cause havoc. you can even go into their dungoens.

Haven't the mods kind of declared this subject off-limits for now?

And more on-topic, no it currently isn't possible, and to attempt to implement it now would interfere with ZOS's design goals in the game and delay the release of the game by a few months.

Thing is that the war between factions is not being fought to conquer each other, but to gain control of the White Gold Tower and the throne. That is the objective of the war. Not to invade each other's homeland

Yeah, this is not open for discussion at this point. The last thread about this ended up rather heated, with people ignoring any posts/information that didn't fit what they wanted to believe.