Is there any open world PVP in this game?

Art this time, I believe there is definitely not. But who knows, Bungie can be persuaded.

I like to think that open world pvp will lead to class being formed on the ground, to guards points of interest and power, all totally unscripted stuff

None right now. The idea is, if you see another player in the open world, you can choose to either help them with what they're doing, or ignore them and continue on your way. Public Events in game are a perfect example of this, but you may be pinned in a
firefight and out of nowhere, another Guardian can show up, save you bacon from the fire, and then disappear like the wind. Cooperation is the key in the open world.

Once you get a few levels under your belt, The Crucible opens to you, and you can have all the PvP action you can handle there.

I've played a couple of MMOs where PvP was apart of the game and although I'm mainly a PvE player I didn't mind the PvP folk. I have been on PvP servers where there has been problems before though. Some MMOs do a better job of handling it then others. I
like the idea of PvP areas but having the whole open world a free for all PvP zone is a recipe for disaster.

Well I have had pc and xbox now with no issues.

Is it during pvp on general open world?

There is actually quite a lot of dialogue and story/lore in this game. Hence it's a mmo'RPG' and not just a normal mmo. They have put a lot of time and effort into the story so it's not just a gear grind for PVE players.

You will meet a mixture of both AI and online players. The online players will be friendly regardless of alliance in the open world as far as I am aware but that is not the case in PvP flagged areas. Pretty sure you cannot engage others in PvP in the open
world.