When you get to lvl 50 and can quest in other factions areas are the quests and mobs scaled to lvl 50 or will it be case if a lvl 50 killing lvl 3 mobs in other factions starting zones?

The mobs will be L50 and higher in those areas.

So does that mean you wont see low players? like an instance just for lvl 50+ players?

Yeah it's a fresh instance only for L50 people and up. You won't be in the same instance as the low level people from that alliance.

It is definitely for the best that L50 people work through zones without other players otherwise those lower level players would simply follow or group up with those higher level players and breeze through the content. Everybody is on equal footing here, apart from when level 50 players help their own alliance members quest through their own zone.

basically is the veteran dungeon version of an world. An pretty smart way of adding more single player content. Yes not as good as two totaly new zones but a couple of light year ahead of daily quests.

But its some danger that you run into an altmer with interest for nimroots at the end of 50++